# What was the first solar eclipse that was demonstrably predicted in advance?

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There is a famous story going back to Herodotus according to which Thales of Miletus predicted the solar eclipse of May 28, 585 BC, which interrupted a battle. Given that we have not a single contemporary source for that claim, and it is unknown how Thales could have even accomplished such a prediction with the methods available to him, the reliability of this claim should be considered doubtful at best.

What, then, is the earliest Solar Eclipse that was verifiably predicted in advance? Certainly, that eclipse occurred no later than May 3, 1715, as Edmond Halley predicted that eclipse, with very high accuracy. But is there any instance before that where an eclipse was successfully predicted?

(This is an incomplete answer since I don't know which eclipse specifically was predicted, nor how it compares to the rest of the world. But it is too long for a comment.)

Because of their cultural association of governmental legitimacy with astronomical/geophysical omens, ancient China was rather obsessed with predicting eclipses. Attempts to do so seemed to have begun in the Warring States era, but naturally were not very successful. Some breakthroughs were achieved in the Eastern Han when it was realised that the moon's motion is inconsistent.

By 20 B.C. the Chinese knew how eclipses were caused… By 8 B.C. the Chinese could predict eclipses by using the 135 month period; and by A.D. 206 they could predict eclipses by analyzing the motion of the moon. By A.D. 390 they could predict how much of the moon would be in shadow.

- Thurston, Hugh, Early Astronomy, Springer, New York, 1994

These are referring to solar eclipses, as was made clear by the rest of the paragraph discussing ancient disputes over how the moon could block the sun's light. See also:

Astronomers were attached to the royal household as second tier functionaries… One of the most important events to predict were eclipses. In the first century B.C. (the Han dynasty), an eclipse period of 135 months was recognized during which 23 eclipses were known. By the third century A.D., the astronomer Yang Wei was able to specify times of first contact for a solar eclipse.

Case Western Reserve University: Journey Through the Galaxy-

By about 20 BC, surviving documents show that Chinese astrologers understood what caused eclipses, and by 8 BC some predictions of total solar eclipse were made using the 135-month recurrence period. By AD 206 Chinese astrologers could predict solar eclipses by analyzing the Moon's motion.

It would therefore appear that, that by about the early third century, at least some eclipses were predicted.

Of course, these predictions were not very good, especially since the sun's movement had not been understood. That happened much later in the Tang Dynasty. The monk Yi Xing was able to produce better eclipse predictions based on his research. Another notable advancement in Chinese astronomy was achieved in the Yuan Dynasty, by the astronomers Wang Xun and Guo Shoujin.

This actual movement of the sun was fully understood by the famous astronomer Yi Xing (一行, 683-727 A.D), and he used the theory in his computations, for example the calculations for the time fo eclipses, in his Da Yan calendar (大衍歷, 729 A.D), getting accurate results in the process.

(… )

Guo and his co-workers were able to make more accurate astronomical calculations, which helped them to make better astronomical predictions, especially in the case of eclipses.

- Tiong, Ngsay, and and Helmer Aslaksen. "Calendars, Interpolation, Gnomons and Armillary Spheres in the Work of Guo Shoujin (1231-1314)."

Again, the eclipse predictions were still not perfect, especially over the course of centuries. However, a failed prediction was cause for commissioning a new calendar. Conversely, this meant that at least some of the predictions even in this early period were accurate, by chance or otherwise.

One major piece of evidence proposed by Xu in favour of the adoption of Western methods concerned eclipse predictions… [E]clipse prediction was the touchstone. In 1610, when it was first proposed to employ Jesuits for astronomical reform, the miscalculation of a solar eclipse was used to make the case for the necessity of this reform.

- Jami, Catherine, et al, eds. Statecraft and Intellectual Renewal in Late Ming China: the Cross-Cultural Synthesis of Xu Guangqi (1562-1633). Vol. 50. Brill, 2001.

At this juncture the then-extant Chinese calendars were failing in their predicative powers. The Court held a competition (to predict an eclipse) between the Chinese court astronomers and the Westerners, which resulted in a resounding victory for European astronomy.

Wikipedia has an informative article on the Saros cycle, which is used to predict eclipses.

According to that page, and by extension apparently the pages to which it references, the Babylonians were recording the eclipses which describe the cycle in the sixth century BC. Apparently Hipparchus (second century BC), Pliny (first century AD) and Ptolemy (second century AD) were aware of the cyclic nature of eclipses, though the degree to which they could be predicted for a specific location is debatable.

Ptolemy ( ca 150 BC)[sic] represents the epitome of Greecian astronomy, and surviving records show that he had a sophisticated scheme for predicting both lunar and solar eclipses. Ptolemy knew, for example, the details of the orbit of the Moon including its nodal points, and that the Sun must be within 20d 41' of the Node point, and that up to two solar eclipse could occur within seven months in the same part of the world. Lunar eclipse were especially easy to calculate because of the vast area covered by the Earth's shadow on the Moon. Solar eclipses, however, required much greater finesse and knowledge. The shadow of the Moon on the Earth is less than 100 kilometers wide, and its track across the daytime hemisphere is the result of many complex factors that cannot be anticipated without a nearly-complete understanding of the lunar orbit and speed.

The writeup (available here) also supports the other answers here and provides a lot of related information. (note that Ptolemy actually lived AD, not BC)

This detailed article argues for the authenticity of Herodotus' report about Thales ecplise prediction in 585 BC. This is in any case a lot earlier than the Chinese material cited by Semaphore.

I am going to second dotancohen's answer somewhat. Hipparchus developed a comprehensive astronomy that accurately predicted eclipses and other astronomical events. Ptolemy's writings emanate from the tradition that was established by Hipparchus.

Nevertheless, Hipparchus was certainly not the beginning of Greek astronomy. He simply formalized and improved it. Long before Hipparchus many Greek philosophers were very capable in astronomy and mathematics, such as Thales of Miletus. Although Herodotus lived 100 years after Thales, there is no specific reason I know of to doubt his claim that Thales predicted his eclipse.

Herodotus says that Thales "discovered" the mechanics of eclipses, so this would suggest he considered this new technology at the time, improvements over the Egyptian and Babylonian methods. It is known that the Babylonians could predict lunar eclipses which is pretty easy, but not solar eclipses and the same is probably true for Egyptians.

Also, remember that ancient scientists had access to lots of writings that are now lost, including material on Thales. None of these contradicted Herodotus or corrected his account. In fact, later Greek astronomers repeatedly confirmed what Herodotus had claimed which is that Thales was the first to do it.

On July 30, 2014, Tony Freeth published his findings in PlosOne, that ancient Greeks were predicting lunar eclipses using the Antikythera Mechanism some time between 250BC and 1BC. Aside from predicting dates, this remarkable device was also able to predict magnitude, color, and obscuration.

## Observations and predictions

A stone from the IX th century at the museum of Xi'an containing the description of the total eclipse of the Sun occurring on July 17, 709 before J.-C. observed at sunset at Ch'u-Fu (Qifu).

A fragment of the 34093 shelf at the British Museum containing the description of the solar eclipse of September 26, 322 before J.C. observed at sunset at Babylon.

## I. The mythological representations

In almost all ancient cultures and societies without writing, a prodigious phenomenon such as an eclipse of the Moon, and more of the Sun, has been reported to a supernatural cause, the intervention of a god, a demon or an evil genius threatens to turn off both lights. A fatal event we usually attempt to stave forcefully with magic formulas to prevent the Moon or the Sun to be eaten forever. In Asia, a celestial dragon was supposezd to be responsible for eclipses (the oldest Chinese word for eclipse, shih, means "eat"). In India, it was Rahu and Ketu, the two parts of a Demon beheaded by Vishnu corresponding ,respectively to the ascending and descending nodes of the Moon when the eclipses occur, seeking to devour the Moon and the Sun. Long in the Western countries, astronomers designate these two nodes that make a complete revolution of the zodiac in 18 years and 6 months under the name Caput Cauda Draconis (Head and Tail of the Dragon). In America, from Canada to Peru through Mexico, and even in Africa, it was such mythical animal or that demon who threatened to eat either the Moon or the Sun. About ancient Greece, it was no exception to the rule. According to Democritus (460-370 before J.C.), eclipses of the Moon and of the Sun were among the terrifying celestial events making men believing that the gods were the perpetrators .

## II. Understanding the eclipse phenomenon

### The legend of Thales

According to a legend firmly established, Thales of Milet (VI th century before J.-C.) would be released very early from the belief in the divine causality of eclipses. In fact, according to the Greek historian Herodotus (about 484-425 BC), Thales had predicted to the Ionians an obscuration of the the Sun "for the year in which it occurred" (Survey I 74). Few authors, both ancient and modern, have questioned that which was held for one of the seven sages, has been able to predict a solar eclipse. According to Pseudo Plutarch (Opinion of philosophers, II 24), Thales understood the nature of the phenomenon ("the solar eclipse occurs when the Moon, whose nature is terrestrial, is placed just under him".) But this would obviously be not enough to move to the infinitely more complex step of the prediction of an eclipse occurring on a specific date and visible in a specified region of the globe. Some historians determined as sure that May 28, 585 BC was the date of the solar eclipse announced by Thales and the American historian O. Neugebauer said that there is no cycle to predict a solar eclipse in a given place, and that around 600 BC, and that the ephemerides compiled by the Babylonians and used by Thales did not contain any theory for predicting eclipses of the Sun. This legend of Thales is as unreliable as the one of Anaxagoras (500-428 BC) who "thanks to his knowledge of astronomical science" (Pliny the Elder, Natural History, II, 149), would have predicted a meteorite fall!

### From Pythagoreans to Aristotle

If solar eclipses are about as numerous as lunar eclipses when one considers the Earth in its entirety, we approximately have twice chance to observe, in a given place, a lunar eclipse. But there are some periods which are more favorable than others to observe solar eclipses in the same region. The Greek historian Thucydides (460- to 395 BC) lived in such a period. He noted that during the Peloponnesian War, the "solar eclipses were more numerous than at any another historical era" (The Peloponnesian War, I 23). This assertion is confirmed by F. Richard Stephenson (see the bibliography), which dates the two solar eclipses mentioned by Thucydides (op. cit. II 28 and IV 52), respectively, on 3 August 431 and 21 March 424 BC. The first eclipse (annular visible from Athens) is described in these terms by the Greek author, which could state to a personal observation: "A New Moon day (this is the only time it seems that this phenomenon can occur) there was in the early afternoon a solar eclipse. The Sun took the form of a crescent and some stars became visible. Then resumed the Sun resumes its normal form".

According to Aristotle (384-322 B.C.), the Pythagoreans, who thought that lunar eclipses were more numerous in absolute that the solar eclipses, tried to explain this by supposing that it was not only the Earth, but another Earth , named anti-Earth facing away ours and that we do not see, which is also interposed between the Moon and its illumination source (Treaty of heaven, II 13). For free as this hypothesis, it assumes that the Pythagoreans, including Philolaos (about 470-390 BC) understood the generam mechanism of eclipses which postulates that the celestial bodies have a spherical shape, that some are opaque and other bright, and that their position relative the Earth, at the surface of which the observer is located, determines the time for a partial or total obscuration of the Moon or the Sun. Concerning Aristotle, it is apparently the first to have mentioned among the "sensitive" evidences of roundness of the Earth that the figure projected on the Moon when eclipsed "during eclipses, the Moon has always as limit a curved line: therefore, as the eclipse is due to the interposition of the Earth, it is the shape of the surface of the Earth that is due to the shape of the line" (Treaty of heaven, II 14).
The different types of solar eclipses.

Geminus (near 50), in his Introduction to the phenomena, X 1-6, appears to offer the first synthetic presentation of the cause and the different types of solar eclipse. It specifies that the transit of the Moon in front of the Sun (that is to say when the Moon is in "synod" or in conjunction with it) causes an interception of sunlight, so it should be better and his remark is correct, to speak in this case of interposition and not of eclipse of the Sun: "in fact never the smallest part of the Sun is eclipsed: it becomes only invisible to us by interposition of the Moon". Geminus adds that consequently, the eclipses are not the same everywhere, and there are large differences in the magnitude of eclipses for different places: at the same time, the Sun is eclipsed completely that is to say for locations in the alignment of the interposition and elsewhere in places located slightly outside line interposition is eclipsed partially still elsewhere, no eclipse is visible.
The prediction: knowledge of cycles and geometric models
This is truly with the Almagest, the greatest astronomical work of antiquity due to the astronomer Claudius Ptolemy (II th century AD), that the calculation of eclipses of the Sun becomes possible, but not yet that of their global zone visibility. It had long been recognized that eclipses of the Sun require two conditions: that the Moon is new and it is close, as the Sun, to one of its nodes. Predicting a solar eclipse presupposes that one has a theory of the motion of the Moon and a theory of the motion of the Sun. If the theory of this motion was not a problem, it was not so in the case of the Moon. Our satellite has a complex motion in longitude, affected by many inequalities. The observation had revealed in ancient times the two most important, the equation of the center (already known by Hipparchus) and the evection precisely discovered by Ptolemy. The author of the Almagest knew also that the lunar parallax, which can exceed one degree affects significantly the geocentric latitude of the Moon, that is to say its angular distance to the ecliptic. Finally, Ptolemy knew the apparent diameters of the Sun and the Moon in relation to their distance from Earth. It is this last point that makes the superiority of the Greek astronomy on the Babylonian one. Even at its peak, that is to say, from 300 BC until the beginning of our era, the Babylonian astronomy was not able to predict the possibility or the impossibility of a solar eclipse. The Babylonian ephemerides, which are not based on a geometric pattern, but only on arithmetic functions, are nevertheless able to predict, as well as Ptolemy's the coordinates of the Sun and the Moon. But the lack of data on the relative dimensions of these two bodies prevents the prediction of the visibility of the eclipse.

Calculating a solar eclipse occurs in the Almagest in three steps. At first, Ptolemy calculates the angular distance from the Moon to one of its nodes. These are also not fixed: it was recognized early enough that they moved on the ecliptic, and the observation identified their average period of revolution. All calculations were facilitated by tables, so that it was quite easy to predict from one year to the other, dates where eclipse was possible. They knew that the eclipses occurred every six months, when the Sun crosses a node of the lunar orbit (draconitic year).

Secondly, Ptolemy determined near the date where the eclipse is possible, the time of the conjunction Moon-Sun, ie the time of the New Moon. He has for that a good value of the synodic month (mean interval between two New Moons) which gives him the moment of the average conjunction, and after correction of some inequalities, the time of the true conjunction. At this step of the calculation, it is already possible to say whether or not the eclipse will be visible: a conjunction taking place at night for example is obviously invisible.

From antiquity to the XVII th century, astronomers searched the conditions of eclipse where is the observer and not for the Earth in general, as it is done today in modern astronomy. It is thus calculated, for a certain area in latitude, the conditions of occurrence of the eclipse. This problem, one of the more complex developed in the Almagest is processed using the parallax effects on the ecliptic coordinates of the Moon. Not only the Almagest shows whether the eclipse is partial or total in a some place (the magnitude is expressed in fingers), but also makes it possible to calculate its duration and the moment the first and the last contact.

Just note that Ptolemy never used the period of 223 lunations - improperly named Saros by Edmond Halley - to predict a solar eclipse. A clarification is needed here regarding this period allegedly used by the Babylonians for the prediction ofsolar eclipses. Halley published in 1692 in the Philosophical Transactions a memory in which he proposed to correct a passage of Pliny the Elder (23-79 AD), which concerned a period after which eclipses recur in the same order. Some manuscripts of the Natural History circulating at the time contained variants, and in the one of Halley, it was written: "There is no doubt that eclipses recur in the same order after 222 months [Defectus CCXXII mensibus redire in suos orbs], and that the Sun is eclipsed only when Moon ends or begins its course, that is to say at the moment of the conjunction" (Natural History, II 56). Halley corrected 222 to 223 (CCXXIII). But by looking at the Souda, Byzantine encyclopedia written during the X t century by a group of scholars (which was took a long time for a scientist named Suidas), he found mention of the word in the following terms: " the Saros, measurement and number for the Chaldeans. A lunar saros contains 222 lunar months which make 18 years and six months. 120 saros correspond to 2222 (sic for 2220) years". Mistakenly believing that Souda depended here on Pliny (which does not use the term Saros), Halley concluded that the Babylonians meant thus a period of 223 lunations making the eclipses coming back. But the Souda expressly says that 222 months = 18.5 years, i.e. just a year of 12 months exactly (222/18.5 = 12). But the Babylonian calendar is lunar, and the duration of the months is variable.

In conclusion, the period named Saros by the Babylonians has nothing to do with eclipses. The error made by Halley was denounced by the French astronomer Guillaume Le Gentil in Galaisière (1725-1792) in two articles very critical published in 1756 but it will and not heard since, despite the correction made by many historians of science, the word Saros continues to designate a period of 223 lunar months, or 18 years and 11 days, or 6,585 days, after which eclipses of the Sun and the Moon recur in the same order.

## III. The determination of the zones of visibility of the eclipses of the Sun

The method outlined in the Almagest will suffer almost no change until the seventeenth century. Nevertheless, the famous Arab astronomer Al- Battani (middle of the IX th -929) concludes to the variation of the apparent diameter of the Sun, and therefore to the possibility of annular eclipse of the Sun. Copernicus (1473-1543), in his De revolutionibus orbium Coelestium published in 1543, will take almost point by point the method of Ptolemy, without improvements made. A comprehensive study showed that this method was able to detect virtually all solar eclipses, only the eclipses of faint magnitude affecting polar regions, escaped the investigation of the Ancients.

From the XVI th century, there has been an increase in the publications of ephemerides in Europe, all providing very properly solar eclipses and their visibility. There are also, since the Middle Ages, special tables that predict eclipses very long in advance. The work of Tycho Brahe (1546-1601), and of Kepler (1571-1630), will only increase the accuracy of the theories of the Sun and the Moon this quest for precision will only grow after Newton and the birth of celestial mechanics.

The idea of ​​representing on a map the visibility zone of a solar eclipse appears during the seventeenth century thanks to Jean -Dominique Cassini (1625-1712). This is an important and difficult problem that requires predicting the general eclipse, otherwise said, it is to determine the set of points on the Earth's surface which can actually see one of the phase of given magnitude of the eclipse (partial, annular or total). Edmond Halley had three essential elements in order to achieve such a prediction, namely a good theory of the motions of the Sun and the Moon, an accurate estimate of the distance of the Moon and finally precise geographic coordinates. He left us a remarkable map for the eclipse of the Sun on May 3, 1715 (at right) showing the zone of visibility of the eclipse for the south of England as calculated in advance. Five months later, he ploted the path of totality as it was actually observed on the basis of reports received from various correspondents that Halley had alerted. The difference is of some 20 miles compared to the prediction of Halley.

Credit : All rights reserved Eclipse of the Sun: drawing by Halley of the visibility of the eclipse of May 3, 1715.

During the XIX th century, the German astronomer Friedrich Bessel (1784-1846) will develop a method still in use, to facilitate the calculation of local circumstances and conditions of visibility of a solar eclipse. All these developments were mainly possible due to ever-improving knowledge of the distance Earth-Moon and Earth-Sun since the XVII th century. But even in the early twentieth century the precise plot of the entire strip of totality included uncertainties of a few kilometers due to the imperfection of the theory of the Moon to which should be added, as discussed below, the irregularities of the own rotation of the Earth.

Credit : Observatoire de Paris Eclipse of the Sun : drawing from Theoricae novae planetarum of Georg peurbach, Paris, 1543.

## IV. The historical eclipses

We conclude with some examples that demonstrate that the knowledge of solar eclipses in the past is useful not only for historians of astronomy, but also historians and astronomers.

We will discuss first how was treated by astronomical science of the Middle Ages the case of an eclipse of a very special kind. From the De Sphaera of Jean Sacrobosco (XIII th century) a treaty which will be read and commented until the XVII th century, ending on the following question, arrising from the reading a passage of the Gospels: " When it was the sixth hour, there was darkness over the whole land until the ninth hour" (Gospel of Mark, 15, 33). The question was to know whether the solar eclipse that took place during the Lord's Passion was natural or miraculous. Matter that the Ptolemaic theory of eclipses perfectly assimilated by medieval astronomers allowed to make a response free of ambiguity: it could not be a natural phenomenon since eclipse necessarily occurs when the Moon is new: Christ was crucified during Passover when the Moon was full commentators of Sacrobosco added in the same idea the unusual length of the eclipse. It was, therefore, a miracle through which the omnipotence of God manifested itself. A legend (which confuses several characters named Denys) states that learning from the Apostle Paul the true nature of the darkening of the sky he had observed in Athens, Dionysius Areopagite converted himself to Christianity, moved to France, where he would have converted the inhabitants and became bishop of Paris where he would have ended martyr.

The mention of an exceptional or spectacular celestial phenomenon, accompanying a religious, political or military event, and intended to highlight its importance were also frequently associated to comets for this purpose: it is not uncommon in the ancient chronicles. But the precise knowledge of solar eclipses which occurred in the past allows historians to verify and possibly invalidate the stories of some authors. This is for example the case for the eclipse mentioned by the Byzantine historian Zosimus (end of the V th - early VI th century) in his new History (IV, 58). About the battle which took place on September 5, 394 in the Julian Alps between Eugene, Arbogast and Theodosius, Zosimus wrote: "when Eugene marched against them with all his troops and when the armies came to blows with each other, it occurred at the same time of the battle a solar eclipse so complete that it seemed rather night than day for considerable a period of time". The indication by Zozimus of an eclipse lasted a considerable time is suspect, and for good reason: there was no eclipse on September 5, 394 !

We may also, from a solar eclipse, date an event on which the manuscript sources do not provide chronological indications more or less ambiguous. For a long time, the exact year of the death of the Emperor of the West, Louis I the Pious, son of Charlemagne was ignored. We only had the testimony recorded in a medieval chronicle from which the year when the Emperor Louis died "there was an eclipse of the Sun on Wednesday before Ascension" (eclipsis solis facta is IV feria ante ascensionem domini). However, the calculation shows a total eclipse of the Sun was visible in Europe on May 5, 840, the eve of the Ascension. So, the Emperor is dead in 840.

## V. Ancient eclipses and modern methods of analysis

The astronomers do not use today the eclipses of the Sun to improve the theory of celestial mechanics, but they continue to draw key lessons from ancient eclipses. In 1749, the English astronomer Richard Dunthorne (1711-1775) used eclipses mentioned by Ptolemy. Recalculating these eclipses, Dunthorne brought to light a regular disagreement between the calculated and observed moments: the motion of the Moon seemed to accelerate of 20" per century. It is only during the XIX th century that the problem was solved: it is not the Moon which accelerates, but it is the Earth that rotates more slowly around its axis due to the friction of seas on the ocean floor. Since the rotation of the Earth slows steadily regardless of seasonal irregularities, the subsequent calculation of ancient eclipses must therefore take into account this slowdown, under penalty of large shifts. It is known for example from Babylonian sources that a total solar eclipse took place at Babylon on April 15, 136 BC. If we recalculate with modern theories, the circumstances of the eclipse regardless of the slowdown of the rotation of the Earth, it is found that the entire band of total visibility passed not to Babylon (located in present-day Iraq about 160 km south of Baghdad), but in Morocco as seen on the map below. We see from this example and from many other recently studied masterfully by F. Richard Stephenson that today astronomers benefit greatly observations of ancient eclipses to highlight the changes in the rotation of the Earth. Thus, the Earth slows 1.6 millisecond per century (i.e. the length of the day increases of 1.6 ms per century), which, cumulated, give a difference of about 4 hours for the eclipse of Babylon. It also shows the limits of the current celestial mechanics for any prediction of the path of totality of an eclipse of the Sun. It cannot, across centuries, be absolutely accurate because of irregularities in the rotation of our planet impossible to determine in advance.

## VI. The last total eclipses observed in France

On 22 May 1724, a total eclipse visible in Paris occurred. It took place from 17h 42m to 19h 29m Universal Time. It was complete in Paris between 18h 35m 18h 38m 45s and 13s is for a period of 2m 28s. Below the map of the prediction made ​​at that time.

Credit : Observatoire de Paris

On April 17, 1912, a central annular eclipse, total for some places because of the variation of the Earth-Moon distance, was observed in the Paris region. The totality was visible only on a line passing west of Paris near 12h 20m (Paris civil time). However, on the Belgian part of the path and further north, the eclipse was visible as a annular. Outside this line, the eclipse was seen as partial. Below is the map showing the A-B line of observation.

Credit : Annuaire du Bureau des longitudes

On February 15, 1961, a total solar eclipse took place in the south of France, at sunrise. Below is the visibility zone maps and schedules.

Credit : Annuaire du Bureau des longitudes

On August 11, 1999, a total eclipse was visible just north of Paris between 10h 20m and 10h 30m Universal Time. Unfortunately clouds were present during the observation of this phenomenon.

Some explanations on the phenomena "eclipse of the Sun" and "eclipse of the Moon"

## How a solar eclipse first proved Einstein right (Synopsis)

"Eddington had needed to make significant corrections to some of the measurements, for various technical reasons, and in the end decided to leave some of the Sobral data out of the calculation entirely. Many scientists were suspicious that he had cooked the books. Although the suspicion lingered for years in some quarters, in the end the results were confirmed at eclipse after eclipse with higher and higher precision." -Peter Coles

If ever you attempt to come out with a new scientific theory, there are three criteria you must fulfill:

1. You must reproduce all the successes of the old theory, the one you're looking to replace.
2. You must explain at least one observation or measurement, successfully, that the old theory failed to explain.
3. You must make a new prediction, different from the old theory's prediction, that you can go out and test.

When Einstein's General Relativity first came out, it met those first two criteria, but the third proved exceedingly difficult.

During a total eclipse, stars would appear to be in a different position than their actual locations, due to the bending of light from an intervening mass: the Sun. Image credit: E. Siegel / Beyond the Galaxy.

The only practical test that people could come up with involved measuring the position of distant stars during the day: very close to the Sun. According to Einstein, the curved space around a large mass would bend the starlight, causing its position to shift in a measurable way. While VLBI radio observations can do this today, there was no such technology a century ago. And yet, a total solar eclipse made exactly those critical observations possible.

Actual negative and positive photographic plates from the 1919 Eddington Expedition, showing (with lines) the positions of the identified stars that would be used for measuring the light deflection due to the Sun's presence. Image credit: Eddington and Sobral, 1919.

### More like this

Even fanatic Einsteinians (Sabine Hossenfelder, Brian Greene, Stephen Hawking) admit that Eddington's 1919 results were inconclusive and even fraudulent:

Sabine Hossenfelder: "His measurements had huge error bars due to bad weather and he also might have cherry-picked his data because he liked Einstein's theory a little too much. Shame on him."

People outside Einsteiniana are much franker:

Frederick Soddy (1921 Nobel Prize in chemistry for his research in radioactive decay and particularly for his formulation of the theory of isotopes): "Incidentally the attempt to verify this during a recent solar eclipse, provided the world with the most disgusting spectacle perhaps ever witnessed of the lengths to which a preconceived notion can bias what was supposed to be an impartial scientific inquiry. For Eddington, who was one of the party, and ought to have been excluded as an ardent supporter of the theory that was under examination, in his description spoke of the feeling of dismay which ran through the expedition when it appeared at one time that Einstein might be wrong! Remembering that in this particular astronomical investigation, the corrections for the normal errors of observation - due to diffraction, temperature changes, and the like - exceeded by many times the magnitude of the predicted deflection of the star's ray being looked for, one wonders exactly what this sort of "science" is really worth."

In 1919 Arthur Eddington was a solitary fraudster but a few years later he was already a gang boss:

Quote: "Consider the case of astronomer Walter Adams. In 1925 he tested Einstein's theory of relativity by measuring the red shift of the binary companion of Sirius, brightest star in the sky. Einstein's theory predicted a red shift of six parts in a hundred thousand Adams found just such an effect. A triumph for relativity. However, in 1971, with updated estimates of the mass and radius of Sirius, it was found that the predicted red shift should have been much larger – 28 parts in a hundred thousand. Later observations of the red shift did indeed measure this amount, showing that Adams' observations were flawed. He "saw" what he had expected to see."

Quote: "In January 1924 Arthur Eddington wrote to Walter S. Adams at the Mt. Wilson Observatory suggesting a measurement of the "Einstein shift" in Sirius B and providing an estimate of its magnitude. Adams' 1925 published results agreed remarkably well with Eddington's estimate. Initially this achievement was hailed as the third empirical test of General Relativity (after Mercury's anomalous perihelion advance and the 1919 measurement of the deflection of starlight). It has been known for some time that both Eddington's estimate and Adams' measurement underestimated the true Sirius B gravitational redshift by a factor of four."

Quote: ". Eddington asked Adams to attempt the measurement. [. ] . Adams reported an average differential redshift of nineteen kilometers per second, very nearly the predicted gravitational redshift. Eddington was delighted with the result. [. ] In 1928 Joseph Moore at the Lick Observatory measured differences between the redshifts of Sirius and Sirius B. [. ] . the average was nineteen kilometers per second, precisely what Adams had reported. [. ] More seriously damaging to the reputation of Adams and Moore is the measurement in the 1960s at Mount Wilson by Jesse Greenstein, J.Oke, and H.Shipman. They found a differential redshift for Sirius B of roughly eighty kilometers per second."

Pentcho - It's fairly easy to find scientists from the era 1915 - 1923 who denigrated Einstein and his theories. There was an active group that fought a long hard battle to deny the Nobel prize to Einstein. They were motivated partly from anti-semitism and partly from reluctance to embrace a strange theory that many simply didn't understand. In quoting these old sources, there's an obligation to recognize the biases held by the speaker. By the time of the quote above, Soddy had left active scientific work and was engaged in somewhat strange political pursuits, and wrote several papers expressing anti-semitic views.

Anti-semitism is irrelevant here. I have also quoted Sabine Hossenfelder - she is not an anti-Semite but essentially confirms Soddy's words. Actually Soddy is the only "old source" I quote. Here are new sources:

Discover: "The eclipse experiment finally happened in 1919. Eminent British physicist Arthur Eddington declared general relativity a success, catapulting Einstein into fame and onto coffee mugs. In retrospect, it seems that Eddington fudged the results, throwing out photos that showed the wrong outcome. No wonder nobody noticed: At the time of Einstein's death in 1955, scientists still had almost no evidence of general relativity in action."

New Scientist: "Enter another piece of luck for Einstein. We now know that the light-bending effect was actually too small for Eddington to have discerned at that time. Had Eddington not been so receptive to Einstein's theory, he might not have reached such strong conclusions so soon, and the world would have had to wait for more accurate eclipse measurements to confirm general relativity."

Stephen Hawking: "Einsteins prediction of light deflection could not be tested immediately in 1915, because the First World War was in progress, and it was not until 1919 that a British expedition, observing an eclipse from West Africa, showed that light was indeed deflected by the sun, just as predicted by the theory. This proof of a German theory by British scientists was hailed as a great act of reconciliation between the two countries after the war. It is ionic, therefore, that later examination of the photographs taken on that expedition showed the errors were as great as the effect they were trying to measure. Their measurement had been sheer luck, or a case of knowing the result they wanted to get, not an uncommon occurrence in science."

Another piece by Ethan in praise of Einstein. (Thanks, P. V. for the reality check. obviously not welcome here.)

Ethan: " According to Einstein, the curved space around a large mass would bend the starlight, causing its
position to shift in a measurable way."

There is another explanation for light being bent as it travels past massive objects: "The Force of Gravity," which Einstein denied as he applied Minkowski's geometrical MODEL, malleable spacetime. since he could not believe that gravity is a force reaching across "empty space". that unbelievable "spooky action at a distance."

The model was an improvement (over Newtonian physics) as a math concept for predicting trajectories, but nobody dares to say what space or time or spacetime actually IS (as a malleable entity in the real world. What real world?!)

There is no ontology of "spacetime," not that physics ever cares about "what it IS" if there is no real world independent of variations in observation.

Ps: They say that light has no "resting mass." Maybe that's because it never "rests!" It's kinetic energy (as momentum) equals mass and can push on solar sails. and be deflected by THE FORCE OF GRAVITY without "curved space" as an ironclad Einsteinian doctrine/ invention.

But the indoctrinated keep chanting in praise of Einstein.

“According to Einstein, the curved space around a large mass would bend the starlight, causing its position to shift in a measurable way.”

Isn’t space curving around a large mass like water or air curving around a mass?
Space isn’t really empty, is it?

Well, Einstein did produce a theory that does agree with observation and experiment. Every test of the theory to date so far has been successful. You rely on it every day whenever you use GPS to navigate. If GPS didn't take Einstein's prediction of gravitational time dilation into account then the positions calculated by GPS would be wrong and the system would be completely unworkable.

Where's your competing theory that does all those the three things that Ethan has succinctly laid out for us?

@skl:
"Isn’t space curving around a large mass like water or air curving around a mass?"

Realize if that was true objects would bend spacetime outward, instead of inward which is what really happens.
So the sign of curvature would be reversed and so the nature of the lens effect. (I think the observed star that is near sun during a solar eclipse, would get closer to sun instead of getting farther away like actually happens.)

Anonymous Coward wrote: "Well, Einstein did produce a theory that does agree with observation and experiment. Every test of the theory to date so far has been successful. You rely on it every day whenever you use GPS to navigate. If GPS didn’t take Einstein’s prediction of gravitational time dilation into account then the positions calculated by GPS would be wrong and the system would be completely unworkable."

Not true. Alleged confirmations of Einstein's relativity are either fraudulent or inconclusive. The GPS fraud: One calculates the distance between the satellite and the receiver by multiplying the time by Einstein's constant speed of light, obtains a wrong value (because the speed of light is variable, not constant), "adjusts the time" in order to fix the wrongness, and finally Einsteinians inform the gullible world that Einstein's relativity (time dilation) is gloriously confirmed:

Quote: "Your GPS unit registers the exact time at which it receives that information from each satellite and then calculates how long it took for the individual signals to arrive. By multiplying the elapsed time by the speed of light, it can figure out how far it is from each satellite, compare those distances, and calculate its own position. [. ] According to Einstein's special theory of relativity, a clock that's traveling fast will appear to run slowly from the perspective of someone standing still. Satellites move at about 9,000 mph - enough to make their onboard clocks slow down by 8 microseconds per day from the perspective of a GPS gadget and totally screw up the location data. To counter this effect, the GPS system adjusts the time it gets from the satellites by using the equation here."

Blatantly lying Einsteinians: Einstein was able to predict, WITHOUT ANY ADJUSTMENTS WHATSOEVER, that the orbit of Mercury should precess by an extra 43 seconds of arc per century:

Jose Wudka, UC Riverside: "This discrepancy cannot be accounted for using Newton's formalism. Many ad-hoc fixes were devised (such as assuming there was a certain amount of dust between the Sun and Mercury) but none were consistent with other observations (for example, no evidence of dust was found when the region between Mercury and the Sun was carefully scrutinized). In contrast, Einstein was able to predict, WITHOUT ANY ADJUSTMENTS WHATSOEVER, that the orbit of Mercury should precess by an extra 43 seconds of arc per century should the General Theory of Relativity be correct."

However Michel Janssen (honest in this case) describes endless empirical adjustment (groping, fudging, fitting) until "excellent agreement with observation" was reached:

Ethan, you wouldn't be baiting the resident anti relativity nuts with a post like this now, would you? )

PV and MM, by all means if you guys have the theories/math all worked out to show that the "Einsteinians" are wrong, by all means just follow the procedure that Ethan nicely laid out for you and show the rest of us. Just remember there are a bunch of really smart people"(Sabine Hossenfelder, Brian Greene, Stephen Hawking)" who HAVE DONE THE HARD WORK TO ACTUALLY UNDERSTAND THE THEORY OF RELATIVITY! Or any other commonly accepted theory currently under fire.

I know someone will say don't feed the trolls, and you are right. but this makes me feel better for a while.

rich r wrote: "Ethan, you wouldn’t be baiting the resident anti relativity nuts with a post like this now, would you?"

Why not? I expect him to start a discussion about other important experiments - e.g. Michelson-Morley and Pound-Rebka. Both confirm Newton's emission theory of light and refute Einstein's relativity (mythology says the opposite of course).

The Eddington observation actually was insufficiently precise enough to eliminate the Brans/Dicke theory of relativity. However, experiments performed in the 1970s using one of the early Mars probes showed that Einstein's prediction was within the two standard deviation experimental error while the Brans/Dicke prediction was not. Further refinements have eliminated Brans/Dicke as an explanation for the light deflection.

Of course, the B/D theory was in hot water from the getgo as it required that the interior of the Sun was rotating 10 times as fast as the atmosphere in order to produce a quadrupole moment sufficient to account for a significant fraction of the observed discrepancy of 43 seconds of arc/century which has been attributed to GR.

Ummm, Pentcho, the emission theory of light is conclusively DISPROVEN by a variety of observations. For instance consider binary star systems. When a binary is on one side of its orbit, it's moving toward the earth, on the other side it's moving away. If emission theory were correct, light emitted on one side of the orbit should travel faster with respect to us than the light emitted on the other side. We can now measure light speed quite precisely, precisely enough to observe such differences. When the speed of light emitted by binary star systems is measured, there is no noticeable variation, thus ruling out emission theory. The consistency of emission theory with the MM experiment (or any other experiment) is irrelevant emission theory is ruled out.

Sean T wrote: "The consistency of emission theory with the MM experiment (or any other experiment) is irrelevant emission theory is ruled out."

Even brothers Einsteinians would find this not very clever.

Besides, you have not understood de Sitter's (Brecher's) argument. Study it more diligently!

Again, either you're ignorant or dishonest. DeSitter and Brecher both argued AGAINST emission theory. Both argued that the overtaking of "slow" light by "fast" light over long enough distances would lead to observed anomalies in the dynamics of binary systems. No such anomalies were observed. Brecher's results constrained the independence of the speed of light upon source velocity to within 2 parts per billion. Emission theory is indeed dead.

Ah, now you know something about de Sitter's and Brecher's argument. Quick learner! Bravo!

"Not true. Alleged confirmations of Einstein’s relativity are either fraudulent or inconclusive. "

Bravo. The usual science deniers on ethan's blog (mooney, cft, the aptly named denier) haven't been brave enough to so boldly assert their one denial.

However dicey Eddingtons photographs and measurements were, subsequent tests of light bending around the Sun show that Einstein's theory is spot on.

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## How Edmond Halley Kicked Off the Golden Age of Eclipse Mapping

In 1715, Edmond Halley published a map predicting the time and path of a coming solar eclipse. Today the astronomer is most famous for understanding the behavior of the comet now named for him, but in his lifetime he was a hotshot academic, elected to the Royal Society at age 22 and appointed the second Astronomer Royal in 1720. He was fascinated with the movements of celestial bodies, and he wanted to show the public that the coming event was not a portent of doom, but a natural wonder.

When the Moon’s shadow passed over England, Halley wrote, if people understood what was happening, “They will see that there is nothing in it more than Natural, and nomore than the necessary result of the Motions of the Sun and Moon.”

The map he created shows England with a broad, gray band across it, with a darker patch within that shows how the moon’s shadow would pass over the land. It was simple and clear—a piece of popular media as much as a scientific document. His work heralded what Geoff Armitage, a curator at the British Map Library, calls “the golden age of the eclipse map.”

“True eclipse maps, in the sense of geographical maps showing the track of eclipses, are a phenomenon of the eighteenth century onwards,” Armitage writes in his book The Shadow of the Moon.

Halley’s map of the eclipse of 1715. Edmond Halley/Public domain

Astronomers have studied the patterns of solar eclipses going back millennia and had some success in predicting their arrival. But as 18th-century astronomers sharpened their understanding of the solar system and the motion of the Earth, Moon, and planets, they were able to predict the paths of solar eclipses with unprecedented accuracy. With his original 1715 map, Halley included a plea for observational data—“A Re-quest to the Curious to observe what they could about it, but more especially to note the Time of Continuance of total Darkness.”

His original predictions, it turned out, were off, but only by a bit. After collecting data from his citizen scientists, Halley updated his original map. He had predicted the time of the eclipse to within 4 minutes, but had the track of it off by about 20 miles—surely a disappointment for anyone in that band of uncertainty. But the work remains a remarkable achievement, and he was confident enough in his calculations that the second version of the map included a prediction of a future eclipse, in 1724, as well.

A map of an annular eclipse on February 18, 1736. Image courtesy of the Osher Map Library and Smith Center for Cartographic Education

Part of the reason that 18th-century scientists produced groundbreaking eclipse maps is that there were so many eclipses in this time period—two annular and five total solar eclipses in the British Islands alone, which is a greater frequency than normal. Popular publishers (John Senex and Benjamin Martin, in particular) wanted to produce broadsides that could help inform the public about the terrifying wonder that would cross the sky.

With each eclipse, the maps iteratively improved. For the 1736 annular eclipse, for instance, Thomas Wright, a self-taught astronomer, land surveyor, and instrument maker, created a map that adopted Halley’s design but added visualizations of what the partial eclipse would look like outside the path of totality.

A Dutch eclipse map from 1748. Library of Congress/ 99446121

British scientists weren’t the only ones working to improve predictions and public communication about eclipses. In the 17th century, Dutch astronomers had created some early eclipse maps that set the stage for the 18th-century advances to come. In the 1700s, German scientists excelled at creating maps that focus on particular scientific themes.

With each eclipse to pass over the British Isles, publishers became more savvy about promoting the event to the public. In 1737, mathematician and astronomer George Smith published a predictive eclipse map in The Gentleman’s Magazine, which is thought to be the first eclipse map published in a popular publication (as opposed to as a stand-alone broadside). By 1764, writes historian Alice N. Walters in a 1999 paper, “so many eclipse maps were on the market—each with a different prediction—that one commentator likened the competition between them and their producers to an event quite familiar to the English public: a horse race.”

“The geography of the great solar eclipse of July 14 MDCCXLVIII: exhibiting an accurate map of all parts of the Earth in which it will be visible, with the North Pole, according to the latest discoveries,” 1748. Library of Congress/ 2013593154

In the 19th century, eclipse mapping continued to advance, and accurate predictions became a matter of course. The most scientific maps took on utilitarian aspects and were less likely to have the aesthetic, public-pleasing qualities of their 18th-century forebears. At the same time, though, beautiful data visualizations that tried to communicate the essence of eclipse science started appearing in almanacs as well.

A map of the solar eclipse on April 25, 1846. Library of Congress/ 2013593158 />An eclipse map from 1869. Courtesy the David Rumsey Map Collection

With these maps, the darkening of the sky became a knowable phenomenon and, as Halley hoped, “the suddaine darkness wherein the Starrs will be visible about the Sun, may give no surprize to the people.” Instead of an ominous portent, the solar eclipse became an event to look forward to.

## Contents

The total eclipse had a magnitude of 1.0306 and was visible within a narrow corridor 70 miles (110 km) wide, crossing 14 of the contiguous United States: Oregon, Idaho, Montana, Wyoming, Nebraska, Kansas, Iowa, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina, and South Carolina. [9] [10] It was first seen from land in the U.S. shortly after 10:15 am PDT (17:15 UTC) at Oregon's Pacific coast, and then it progressed eastward through Salem, Oregon Idaho Falls, Idaho Casper, Wyoming Lincoln, Nebraska Kansas City, Missouri St. Louis, Missouri Hopkinsville, Kentucky and Nashville, Tennessee before reaching Columbia, South Carolina about 2:41 pm [11] and finally Charleston, South Carolina. A partial eclipse was seen for a greater time period, beginning shortly after 9:00 am PDT along the Pacific Coast of Oregon. Weather forecasts predicted clear skies in Western U.S. and some Eastern states, but clouds in the Midwest and East Coast. [12]

At one location in Wyoming, a small group of astronomers used telescopic lenses to photograph the sun as it was in partial eclipse, while the International Space Station was also seen to briefly transit the sun. [15] Similar images were captured by NASA from a location in Washington. (See Gallery – partial eclipse section).

During the eclipse for a long span of its path of totality, several bright stars and four planets were visible. The star system Regulus was almost in conjunction with the Sun. Mars was 8° to the right, and Venus 34° right. Mercury was 10° left, and Jupiter 51° left. [16]

This was the first total solar eclipse visible from the United States since that of July 11, 1991 [17] —which was seen only from part of Hawaii [18] —and the first visible from the contiguous United States since 1979. [19] An eclipse of comparable length (up to 3 minutes, 8 seconds, with the longest eclipse being 6 minutes and 54 seconds) occurred over the contiguous United States on March 7, 1970 along the southern portions of the Eastern Seaboard, from Florida to Virginia. [20]

The path of totality of the solar eclipse of February 26, 1979 crossed only the states of Washington, Oregon, Idaho, Montana, and North Dakota. Many enthusiasts traveled to the Pacific Northwest to view the eclipse, since it would be the last chance to view such an eclipse in the contiguous United States for almost four decades. [21] [22]

The August 2017 eclipse was the first with a path of totality crossing the Pacific and Atlantic coasts of the U.S. since 1918. Also, its path of totality made landfall exclusively within the United States, making it the first such eclipse since the country's declaration of independence in 1776. Prior to this, the path of totality of the eclipse of June 13, 1257, was the last to make landfall exclusively on lands currently part of the United States. [23]

The path of the 2017 eclipse crosses with the path of the upcoming total solar eclipse of April 8, 2024, with the intersection of the two paths being in southern Illinois in Makanda Township at Cedar Lake, just south of Carbondale. An area of about 9,000 square miles (23,000 km 2 ), including the cities of Makanda, Carbondale, Cape Girardeau, Missouri, and Paducah, Kentucky, will thus experience two total solar eclipses within a span of less than seven years. [24] The cities of Benton, Carbondale, Chester, Harrisburg, Marion, and Metropolis in Illinois Cape Girardeau, Farmington, and Perryville in Missouri, as well as Paducah, Kentucky, will also be in the path of the 2024 eclipse, thereby earning the distinction of witnessing two total solar eclipses in seven years.

The solar eclipse of August 12, 2045 will have a very similar path of totality over the U.S. to the 2017 eclipse: about 400 km (250 mi) to the southwest, also crossing the Pacific and Atlantic coasts of the country however, totality will be more than twice as long and it will be seen not only in the United States. [25]

### Oregon Edit

– The Corvallis campus of Oregon State University hosted "OSU150 Space Grant Festival: A Total Eclipse Experience", a weekend-long celebration of the eclipse. A watch party was also hosted on campus the day of the eclipse. [26] – Historic Farewell Bend State Recreation Area hosted the RASC: Yukon Centre (Yukon Astronomical Society) and the RASC: Okanagan Centre. Solar viewing and presentations on the eclipse were given along with a dark-sky presentation. [27] – The Salem-Keizer Volcanoes, a Class A baseball team, played a morning game against the visiting Hillsboro Hops that featured the first ever "eclipse delay" in baseball history. [28] – The city sponsored a four-day Solarfest at two locations. [29] – Symbiosis Gathering hosted a seven-day eclipse festival which included rave-style music dubbed "Oregon Eclipse". [30][31][32] – The Polk County Fairgrounds organized a series of events and an eclipse gathering. [33] – The Oregon Museum of Science and Industry hosted an event at the Oregon State Fairgrounds. [34]

### Idaho Edit

– High altitude balloon launches by the USC Astronautical Engineering department and NASA. [35] – The National Monument and Preserve hosted NASA presentations, evening star parties hosted by the Idaho Falls Astronomical Society, and presentations by the New Mexico Chapter of the Charlie Bates Solar Astronomy Project. [35] – Free entertainment and educational seminars and an eclipse-watching event at the Museum of Idaho (an official NASA viewing site) and elsewhere, and a free eclipse-watching event at Melaleuca Field. [36][37] – Brigham Young University Idaho offered a series of eclipse-related educational events. [38] – The city sponsored a five-day festival prior to the eclipse. [39]

### Wyoming Edit

– The Astronomical League, an alliance of amateur astronomy clubs, held its annual Astrocon conference, [40] and there were other public events, called Wyoming Eclipse Festival 2017. [41] – Fort Laramie held an eclipse viewing event, which included a Special "Great American Eclipse" Program. [42] – The biggest Polish expedition conducted as the Great Expedition of Polish Society of Amateur Astronomers was flocked between Riverton and Shoshoni in the central line of totality. [43]

– Entertainment and educational seminars were offered. [44] ABC News reported live from Carhenge during totality. [45] – Nemaha County Hospital hosted an eclipse viewing event, including sharing safety tips from Lifetime Vision Center. [46] – Homestead National Monument of America – Events were held with Bill Nye the Science Guy as well as representatives from NASA on Saturday, Sunday and the day of the eclipse. [47][48] – Stuhr Museum hosted an eclipse viewing event, including the launch of a NASA eclipse observing balloon. [49] – At Haymarket Park, the Lincoln Saltdogs, an independent baseball team in the American Association, defeated the Gary SouthShore RailCats 8–5 in a special eclipse game, with 6,956 in attendance. The game was paused for 26 minutes in the middle of the third inning to observe the eclipse. The Saltdogs players wore special eclipse-themed uniforms that were auctioned off after the game. [50][48]

### Kansas Edit

– Benedictine College hosted thousands in its football stadium. There were students from schools from Kansas, Missouri, Nebraska, and Oklahoma attending, plus numerous other guests who heard from, amongst others, astronomers from the Vatican Observatory. [51]

### Missouri Edit

– The Cosmo Park and the Gans Creek Park were open for the eclipse. [52] There was a watch party on campus for the students of the University of Missouri coordinated by Angela Speck, [53] and the MU Health Care system released eye safety information. [54] – A 5-mile (8 km) bicycle ride from downtown KCMO (where totality only lasted about 30 seconds) to Macken Park in North Kansas City (where totality lasted 1 minute 13 seconds) was organized by KC Pedal Party Club, a local Meetup group. [55] – The city celebrated its 150th anniversary with an eclipse festival. [56] – TotalEclipseofthePark – August 20 educational program featuring NASAGlenn Research Center Hall of Famer Lynn Bondurant, '61, and August 21 watch party organized by Park University. [57] – Hora Eclipse, an Israeli folkdance camp coordinated with the eclipse, was held at YMCA Trout Lodge and Camp Lakewood, near the Mark Twain National Forest. More information at the event's website, especially its post-mortem page. – An event organized by the St. Clair City Chamber of Commerce. [58] – An event organized by Front Page Science was held at Rosecrans Memorial Airport. [59] – David Tipper hosted his Tipper & Friends 4321 electronic music event at Astral Valley Art Park featuring 5 days of music, art, and eclipse viewing. [60]

### Illinois Edit

– Southern Illinois University sponsored many eclipse related educational events, including the two day Crossroads Astronomy, Science and Technology Expo, and viewing at Saluki Stadium. [61]Amtrak ran a special train, the Eclipse Express, from Chicago to Carbondale. [62]NASA EDGE was broadcasting live from Southern Illinois University Carbondale with a four-hour and thirty-minute show (11:45 a.m. – 4:15 p.m. EDT). [63] – A three-day rock festival called Moonstock was headlined by Ozzy Osbourne, who performed during the eclipse. [64] – View the eclipse with the University of Illinois Astronomy Department. [65]

### Kentucky Edit

– Western Kentucky University hosted thousands of K-12 students in its football stadium. [66] At Bowling Green Ballpark, the Bowling Green Hot Rods, a Class A baseball team, played an eclipse game against the visiting West Michigan Whitecaps. [67] – A four-day eclipse festival was held at Jefferson Davis State Historic Site. [68]

### Tennessee Edit

– The City of Athens hosted "Total Eclipse of the Park" at Athens Regional Park, including entertainment, food, and vendors. [69] – Austin Peay State University presented several educational events, including an appearance by astronaut Rhea Seddon. [70] – Tennessee Technological University hosted a solar eclipse viewing party at Tucker Stadium. [6] Cookeville hosted special events from Saturday to Monday. – celebrated the eclipse by hosting BLACKOUT 2017, an eclipse viewing event held in the city square. In addition to the viewing, a selection of food trucks and musical acts which features The Pink Floyd Appreciation Society band who performed Pink Floyd's The Dark Side of the Moon in its entirety prior to the totality event. [71] – At AutoZone Park, the Memphis Redbirds, a Class AAA baseball team, played an eclipse game against the visiting New Orleans Baby Cakes. [67] – offered many special events, including the Music City Eclipse Science & Technology Festival at the Adventure Science Center. [72] The Italian Lights Festival hosted the largest Eclipse Viewing Party in Nashville, a free NASA-Certified Eclipse Event held at the Bicentennial Mall. [73] Two astrophysicists from NASA's Jet Propulsion Laboratory emceed the countdown. [74]

### North Carolina Edit

– Planetarium shows were offered, as well as rides on the Great Smoky Mountains Railroad to an eclipse location. [75] – The eclipse was visible in totality, and classes were cancelled for several hours during the first day of classes at Western Carolina University. [76]
• Rosman – Pisgah Astronomical Research Institute (PARI) hosted a viewing event. The event at PARI has garnered international attention and the visitors included amateur astronomers.

### Georgia Edit

– Viewing at Sanford Stadium at the University of Georgia. [77] – Get off the Grid Festival [78] on three days preceding the eclipse. – Approximately 400 people gathered at the Georgia Guidestones. [79]

### South Carolina Edit

– Viewing at the Green Pond Landing on Lake Hartwell with food trucks, astronomer, and music. Unfortunately clouds blocked the sun at the beginning of totality, but almost completely disappeared throughout. – The College of Charleston hosted NASA's "eclipse headquarters" broadcast as part of an afternoon eclipse viewing celebration on the green behind the campus library. [80] – Viewing at Clemson University. [81] – The South Carolina State Museum hosted four days of educational events, including an appearance by Apollo 16 astronaut Charles Duke. [82] At Spirit Communications Park, the Columbia Fireflies, a Class A baseball team, played an eclipse game against the visiting Rome Braves. [67] – Viewing at Furman University. Events include streaming coverage from NASA, educational activities, and live music. [83] At Fluor Field, the Greenville Drive, a Class A baseball team, played an eclipse game against the visiting West Virginia Power. [67] – Viewing at Dillon Park. Eclipse viewing glasses given away for free. [84] – The clouds blocked the Eclipse that day much like in Anderson.

A partial eclipse was visible across the width of Canada, ranging from 89 percent in Victoria, British Columbia to 11 percent in Resolute, Nunavut. [85] In Ottawa, viewing parties were held at the Canada Aviation and Space Museum. [86] In Toronto, viewing parties were held at the CNE and the Ontario Science Centre. [87]

### Mexico, Central America, Caribbean islands, South America Edit

A partial eclipse was visible from Central America, Mexico, the Caribbean islands, and ships and aircraft in and above the adjacent oceans, [88] as well as the northern countries of South America such as Colombia, Venezuela, and several others. [9]

### Russia Edit

A partial eclipse was visible during sunrise or morning hours in Russian Far East (including Severnaya Zemlya and New Siberian Islands archipelagos). [89] [90] For big cities in Russia, the maximal obscuration was in Anadyr, and it was 27.82%. [91]

### Europe Edit

In northwestern Europe, a partial eclipse was visible in the evening or at sunset. Only those in Iceland, Ireland, Scotland and the Portuguese Azores archipelago saw the eclipse from beginning to end in Wales, England, Norway, the Netherlands, Belgium, France, Spain, and Portugal, sunset occurred before the end of the eclipse. In Germany, the beginning of the eclipse was visible just at sunset only in the extreme northwest of the country. In all regions east of the orange line on the map, the eclipse was not visible. [92]

### West Africa Edit

In some locations in West Africa and western North Africa, a partial eclipse was seen just before and during sunset. [9] The most favorable conditions to see this eclipse gained the Cape Verde Archipelago with nearly 0.9 magnitude at the Pico del Fogo volcano.

A large number of media outlets broadcast coverage of the eclipse, including television and internet outlets. NASA announced plans to offer streaming coverage through its NASA TV and NASA Edge outlets, using cameras stationed on the ground along the path of totality, along with cameras on high-altitude balloons, jets, and coverage from the International Space Station NASA stated that "never before will a celestial event be viewed by so many and explored from so many vantage points—from space, from the air, and from the ground." [93] ABC, CBS, and NBC announced that they would respectively broadcast live television specials to cover the eclipse with correspondents stationed across the path of totality, along with CNN, Fox News Channel, Science, and The Weather Channel. The PBS series Nova presented streaming coverage on Facebook hosted by Miles O'Brien, and aired a special episode chronicling the event—"Eclipse Over America"—later in the day (which marked the fastest production turnaround time in Nova history). [94] [95]

Other institutions and services also announced plans to stream their perspectives of the eclipse, including the Exploratorium in San Francisco, the Elephant Sanctuary of Hohenwald, Tennessee, the Slooh robotic telescope app, and The Virtual Telescope Project. The Eclipse Ballooning Project, a consortium of schools and colleges that sent 50 high-altitude balloons into the sky during the eclipse to conduct experiments, provided streams of footage and GPS tracking of its launches. [93] [96] Contact with one balloon with $13,000 of scientific equipment, launched under the aegis of the LGF Museum of Natural History near Vale, Oregon, was lost at 20,000 feet (6,100 m). Given that the balloon was believed to have burst at 100,000 feet (30,000 m), it could have parachuted down anywhere from eastern Oregon to Caldwell, Idaho (most likely) to Sun Valley, Idaho a$1,000 reward is offered for its recovery. [97]

The National Solar Observatory organized Citizen CATE volunteers to man 60 identical telescopes and instrumentation packages along the totality path to study changes in the corona over the duration of the eclipse.

A viewing party was held at the White House, during which President Donald Trump appeared on the Truman Balcony with First Lady Melania Trump. With the sun partially eclipsed, President Trump looked briefly in the general direction of the sun before using solar viewing glasses. [99]

The eclipse generated reports of abnormal behavior in animal and plant life. Some chickens came out from beneath their coops and began grooming, usually an evening activity. Horses displayed increased whinnying, running, and jumping after the event. Cicadas were reported to grow louder before going silent during totality. Various birds were also observed flying in unusually large formations. Flowers such as the Hibiscus closed their petals which typically happens at night, before opening again after the solar event. [100]

Pornhub, a pornographic video-sharing website provided an unusual sociological and statistical report: its traffic dropped precipitously along the path of totality, so much so that its researchers were themselves surprised. [101]

NASA reported over 90 million page views of the eclipse on its websites, making it the agency's biggest online event ever, beating the previous web traffic record about seven times over. [102]

In the months leading up to the eclipse, many counterfeit glasses were put up for sale. Effective eclipse glasses must not only block most visible light, but most UV and infrared light as well. For visible light, the user should only be able to see the Sun, sunglint reflected off shiny metal, halogen bulbs, the filament in unfrosted incandescent bulbs, and similarly intense sources. Determining whether the glasses effectively block enough UV and infrared light requires the use of spectrophotometer, which is a rather expensive piece of lab equipment. [8] [103]

The eye's retina lacks pain receptors, and thus damage can occur without one's awareness. [104] [105]

The American Astronomical Society (AAS) said products meeting the ISO 12312-2 standard avoid risk to one's eyes, and issued a list of reputable vendors of eclipse glasses. The organization warned against products claiming ISO certification or even citing the same number, but not tested by an accredited laboratory. Another problem was counterfeits of reputable vendors' products, some even claiming the company's name such as with American Paper Optics which published information detailing the differences between its glasses and counterfeits. [106] [104]

Andrew Lund, the owner of a company which produces eclipse glasses, noted that not all counterfeit glasses were necessarily unsafe. He stated to Quartz that the counterfeits he tested blocked the majority of harmful light spectrum, concluding that "the IP is getting ripped off, but the good news is there are no long-term harmful effects." [103] As one example, the Springdale Library in metropolitan Pittsburgh, Pennsylvania, accidentally passed out dozens of pairs of counterfeit eclipse glasses, but as of August 23 had not received any reports of eye damage. [107]

On July 27, 2017, Amazon required all eclipse viewing products sold on its website have a submission of origin and safety information, and proof of an accredited ISO certification. In mid-August 2017, Amazon recalled and pulled listings for eclipse viewing glasses that "may not comply with industry standards", and gave refunds to customers who had purchased them. [108] [8]

Lensrentals, a camera rental company based in Tennessee, reported that many of its customers returned cameras and lenses with extensive damage. The most common problem reported was damage to the camera's sensor. This most often happens when shooting in live view mode, where the sensor is continuously exposed to the eclipse image and becomes damaged by the sun's light. Another problem was the heat and brightness of the eclipse destroying the lens iris, which mechanically regulates the amount of light that enters the camera. Another problem reported was one of a cinema camera's neutral-density filter being damaged by the heat and light of the eclipse. The cost of all of this damage likely amounted to thousands of dollars. [109]

Officials inside and near the path of totality planned – sometimes for years – for the sudden influx of people. [110] Smaller towns struggled to arrange viewing sites and logistics for what could have been a tourism boom or a disaster. [111]

In the American West, illegal camping was a major concern, including near cities like Jackson Hole, Wyoming. [7] Idaho's Office of Emergency Management said Idaho was a prime viewing state, and advised jurisdictions to prepare for service load increases nearly every hotel and motel room, campground, and in some cases backyards for nearly 100 miles (160 km) north and south of the path of totality had been reserved several months, if not years, in advance. [112] The state anticipated up to 500,000 visitors to join its 1.6 million residents. [113]

Oregon deployed six National Guard aircraft and 150 soldiers because the influx of visitors coincided with the state's fire season. [114] Hospital staffing, and supplies of blood and anti–snake bite antidote, were augmented along the totality line. [115]

Also in Oregon, there were reports of hoteliers canceling existing reservations made at the regular market rate and increasing their rate, sometimes threefold or more, for guests staying to view the eclipse. [116] The Oregon Department of Justice (DOJ) investigated various complaints and reached settlements with affected customers of at least 10 hotels in the state. [117] These settlements included refunds to the customers and fines paid to the DOJ. [118]

Although traffic to areas within the path of totality was somewhat spread out over the days prior to the eclipse, [119] there were widespread traffic problems across the United States after the event ended. Michael Zeiler, an eclipse cartographer, had estimated that between 1.85 million and 7.4 million people would travel to the path of the eclipse. [120]

In Oregon, because an estimated one million people were expected to arrive, the Oregon National Guard was called in to help manage traffic in Madras along US 26 and US 97. [121] Madras Municipal Airport received more than 400 mostly personal planes that queued for hours while waiting to leave after the eclipse. [122]

Officials in Idaho, where the totality path crossed the center of the state, began planning for the eclipse a year in advance. The state Transportation Department suspended construction projects along Interstate 15, which traverses Eastern Idaho, from August 18–22 in order to have all lanes open [123] their counterparts in neighboring Utah, where many were expected to travel the 220 miles (350 km) north via the highway from the Salt Lake City metropolitan area, did the same. On the morning of the eclipse, many drivers left before dawn, creating traffic volume along I-15 normally not seen until morning rush hour northbound traffic on the interstate in Box Elder County north of Salt Lake City slowed to 10–15 miles per hour (16–24 km/h). [124] The Idaho State Police (ISP) stationed a patrol car along I-15 every 15 miles (24 km) between Shelley and the Utah border. [125]

After the eclipse, traffic more than doubled along I-15 southbound, with extensive traffic jams continuing for eight hours as viewers who had traveled north into the totality path from Utah returned there and to points south. The ISP tweeted a picture of bumper-to-bumper traffic stalled on the interstate just south of Idaho Falls. Motorists reported to local news outlets that it was taking them two hours to travel the 47 miles (76 km) from that city to Pocatello to the south, a journey that normally takes 45 minutes. [124] Others reported that it took three hours to travel from Idaho Falls to the closer city of Blackfoot, 30 miles (48 km) farther north of Pocatello. [126]

In the rest of the state the impact was less severe. Traffic nearly doubled on US 93, and was up 55 percent on US 20. [127]

For some northbound travelers on I-15, the Montana Department of Transportation had failed to make similar plans to those in Idaho, scheduling a road construction project to begin on August 21 that narrowed a section of the highway to a single northbound lane, near the exit to Clark Canyon Dam south of Dillon. Though that stretch of highway generally has a traffic count of less than 1,000 vehicles per day, on the day of the eclipse there were over a thousand vehicles per hour at peak times. As a result, traffic backed up as far as Lima, creating a delay of at least an hour for travelers heading northward. Further, as construction had not yet begun, drivers observed cones set up but no workers present on the road. While the state traditionally halts construction projects during high traffic periods, a state official admitted "we . probably made a bad mistake here in this regard." [119]

In Wyoming, estimates were that the population of the state, officially 585,000, may have doubled or even tripled, with traffic counts on August 21 showing 536,000 more cars than the five-year average for the third Monday in August a 68 percent increase. One official offered an estimate of "two people in every car" to arrive at a one-million-visitor figure, and others noted that one million was a conservative estimate based on a one-day traffic count of limited portions of major highways. There were additional arrivals by aircraft, plus travelers who arrived early or stayed for additional days. [128] Two days before the eclipse, traffic increased 18 percent over a five-year average, with an additional 131,000 vehicles on the road. [129] Sunday saw an additional 217,000-vehicle increase. [128]

Following the eclipse, more than 500,000 vehicles traveled Wyoming roads, creating large traffic jams, particularly on southbound and eastbound highways. [130] Drivers reported that it took up to 10 hours to travel 160 miles (260 km) into northern Colorado. [128] There was one traffic fatality, [131] and another fatality related to an off-highway ATV accident, but in general there were far fewer incidents and traffic citations than authorities had anticipated. [132]

In Tennessee, the Knoxville News Sentinel described the traffic problems created by the eclipse as the worst ever seen in that part of the state. One backup along Interstate 75 reached 34 miles (55 km) in length, between Niota and the Interstate 40 interchange at Farragut. A spokesman for the state's Department of Transportation allowed that the traffic jams were the worst he had seen in six and a half years on the job, noting that accidents had aggravated the already heavy traffic flows, attributed the I-75 congestion to Knoxville-area residents heading for the totality path at Sweetwater and returning during what was the city's normal afternoon rush hour. [133]

Before the eclipse, state officials had described their traffic expectations as equivalent to that generated by the Bonnaroo Music Festival, the twice-a-season NASCAR Cup Series races at Bristol or the formerly-held Boomsday fireworks festival. "Maybe they should have considered a tsunami of traffic combining all three of those heavily attended events", the News Sentinel commented. The Tennessee Highway Patrol made sure that "[e]very trooper not on sick leave or military leave or pre-approved leave [wa]s working" the day of the eclipse the state DOT made sure its full complement of emergency-aid HELP trucks were available as well. Alert signs on the highways also warned motorists not to pull over onto the shoulders to watch the eclipse as it could increase the risk of dangerous accidents and block the path of emergency vehicles. [133]

In North Carolina, the Department of Transportation added cameras, message boards and safety patrols in the counties where the total eclipse would take place, as well as stopping road work. The department warned that due to "unprecedented" traffic ordinary activities requiring driving might prove difficult, and advised people to act as if there were snow. [134]

In Kentucky, particularly around the Hopkinsville area, which was dubbed "Eclipseville, USA", [135] post-eclipse traffic caused extensive delays. The en masse departure of tourists via Interstate 69 as well as the Western Kentucky Parkway resulted in commute times double or even triple of normal. [136] [137] The Hopkinsville-to-Lexington commute under normal circumstances lasts three and a half hours.

An eclipse causes a reduction of solar power generation where the Moon shadow covers any solar panel, as do clouds.

The North American Electric Reliability Corporation predicted minor impacts, [138] and attempted to measure the impact of the 2017 eclipse. [139] In California, solar power was projected to decrease by 4–6,000 megawatts [140] at 70 MW/minute, and then ramp up by 90 MW/minute as the shadow passes. CAISO's typical ramp rate is 29 megawatts per minute. [141] Around 4 GW mainly in North Carolina and Georgia were expected to be 90 percent obscured. [140]

After the 2017 eclipse, grid operators in California reported having lost 3,000–3,500 megawatts of utility-scale solar power, which was made up for by hydropower and gas reliably and as expected, [142] [143] mimicking the usual duck curve. Energy demand management was also used to mitigate the solar drop, [144] and NEST customers reduced their demand by 700 MW. [145]

NV Energy prepared for the solar eclipse months in advance and collaborated with 17 western states. When the eclipse began covering California with partial darkness, which reduced its usual amount of solar-generated electricity, NV Energy sent power there. Likewise, when Nevada received less sunlight, other west coast states supplied electricity to it. During the solar eclipse, the state of Nevada lost about 450 megawatts of electricity, the amount used by about a quarter million typical residences.

The 2015 eclipse caused manageable solar power decreases in Europe [146] in Germany, solar power dropped from 14 GW to 7 GW, of a 38 GW solar power capacity. [147]

On June 20, 2017, the USPS released the first application of thermochromic ink to postage stamps in its Total Eclipse of the Sun Forever stamp to commemorate the eclipse. [148] [149] When pressed with a finger, body heat turns the dark image into an image of the full moon. The stamp was released prior to August 21, so uses an image from the eclipse of March 29, 2006 seen in Jalu, Libya. [149]

Animation showing shadow movement of event from space.

Illustration showing umbra (black oval), penumbra (concentric shaded ovals), and path of totality (red).

Illustration featuring several visualizations of the event.

Short time-lapse showing umbra as it moves across the clouds.

Video of the moment totality occurred in Newberry, South Carolina

### Totality Edit

(Images where the sun is completely eclipsed by the moon)

Sequence starting at 9:06 am, totality at 10:19 am, and ending at 10:21 am PDT, as seen from Corvallis, Oregon

Totality and prominences as seen from Glenrock, Wyoming

Totality as seen from Saint Paul, Clarendon County, South Carolina

Totality as seen from Grand Teton National Park, Wyoming

### Transition Edit

(Images showing Baily's beads or a Diamond ring, which occur just as totality begins or ends)

Beginning of Diamond ring as seen from Glenrock, Wyoming

Diamond ring (with large flare) as seen from Cullowhee, NC

### Partial Edit

(Images where the sun is partially eclipsed by the moon)

North Cascades National Park, Washington. The ISS is visible as it transits the sun during the eclipse (4 frame composite image).

Mira Mesa in San Diego, California

Maine at 2:41 p.m. EDT before maximum 68% coverage at 2:45 p.m.

Ellicott City, Maryland shortly before maximum eclipse (

### Images produced by natural pinholes Edit

(Images of the eclipse created by natural pinholes formed by tree leaves)

North Cascade mountains (British Columbia and Washington).

### Views outside of the US Edit

Occurring only 3.2 days after perigee (Perigee on Friday, August 18, 2017), the moon's apparent diameter was larger during the total solar eclipse on Monday, August 21, 2017.

### Solar eclipses ascending node 2015–2018 Edit

Astronomers Without Borders began collecting eclipse glasses for redistribution to Latin America for the total solar eclipse occurring on July 2, 2019, and to Asia for the annular eclipse on December 26, 2019. [150]

A partial lunar eclipse took place on August 7, 2017, in the same eclipse season. It was visible over Africa, Asia, Australia, and eastern Europe.

### Solar eclipses 2015–2018 Edit

This eclipse is a member of a semester series. An eclipse in a semester series of solar eclipses repeats approximately every 177 days and 4 hours (a semester) at alternating nodes of the Moon's orbit. [151]

Solar eclipse series sets from 2015–2018
Descending node Ascending node
Saros Map Gamma Saros Map Gamma
120

Longyearbyen, Svalbard
2015 March 20

Total
0.9453
Solar Dynamics Observatory

2015 September 13

Partial
-1.1004
130

Balikpapan, Indonesia
2016 March 9

Total
0.2609 135

L'Étang-Salé, Réunion
2016 September 1

Annular
-0.3330
140

Partial from Buenos Aires
2017 February 26

Annular
-0.4578 145

Casper, Wyoming
2017 August 21

Total
0.4367
150

Partial from Olivos, Buenos Aires
2018 February 15

Partial
-1.2117 155

Partial from Huittinen, Finland
2018 August 11

Partial
1.1476
Partial solar eclipses on July 13, 2018, and January 6, 2019, occur during the next semester series.

### Saros series 145 Edit

This solar eclipse is a part of Saros cycle 145, repeating every 18 years, 11 days, 8 hours, containing 77 events. The series started with a partial solar eclipse on January 4, 1639, and reached a first annular eclipse on June 6, 1891. It was a hybrid event on June 17, 1909, and total eclipses from June 29, 1927, through September 9, 2648. The series ends at member 77 as a partial eclipse on April 17, 3009. The longest eclipse will occur on June 25, 2522, with a maximum duration of totality of 7 minutes, 12 seconds. All eclipses in this series occurs at the Moon's ascending node.

Series members 10–32 occur between 1801 and 2359
10 11 12

April 13, 1801

April 24, 1819

May 4, 1837
13 14 15

May 16, 1855

May 26, 1873

June 6, 1891
16 17 18

June 17, 1909

June 29, 1927

July 9, 1945
19 20 21

July 20, 1963

July 31, 1981

August 11, 1999
22 23 24

August 21, 2017

September 2, 2035

September 12, 2053
25 26 27

September 23, 2071

October 4, 2089

October 16, 2107
28 29 30

October 26, 2125

November 7, 2143

November 17, 2161
31 32 33

November 28, 2179

December 9, 2197

December 21, 2215
34 35 36

December 31, 2233

January 12, 2252

January 22, 2270
37 38 39

February 2, 2288

February 14, 2306

February 25, 2324
40

March 8, 2342

### Inex series Edit

This eclipse is a part of the long period inex cycle, repeating at alternating nodes, every 358 synodic months (≈ 10,571.95 days, or 29 years minus 20 days). Their appearance and longitude are irregular due to a lack of synchronization with the anomalistic month (period of perigee). However, groupings of 3 inex cycles (≈ 87 years minus 2 months) comes close (≈ 1,151.02 anomalistic months), so eclipses are similar in these groupings.

Inex series members between 1901 and 2100:

November 11, 1901
(Saros 141)

October 21, 1930
(Saros 142)

October 2, 1959
(Saros 143)

September 11, 1988
(Saros 144)

August 21, 2017
(Saros 145)

August 2, 2046
(Saros 146)

July 13, 2075
(Saros 147)

### Metonic series Edit

The metonic series repeats eclipses every 19 years (6939.69 days), lasting about 5 cycles. Eclipses occur in nearly the same calendar date. In addition, the octon subseries repeats 1/5 of that or every 3.8 years (1387.94 days). All eclipses in this table occur at the Moon's ascending node.

21 eclipse events, progressing from south to north between June 10, 1964, and August 21, 2036
June 10–11 March 27–29 January 15–16 November 3 August 21–22
117 119 121 123 125

June 10, 1964

March 28, 1968

January 16, 1972

November 3, 1975

August 22, 1979
127 129 131 133 135

June 11, 1983

March 29, 1987

January 15, 1991

November 3, 1994

August 22, 1998
137 139 141 143 145

June 10, 2002

March 29, 2006

January 15, 2010

November 3, 2013

August 21, 2017
147 149 151 153 155

June 10, 2021

March 29, 2025

January 14, 2029

November 3, 2032

August 21, 2036

Notable total solar eclipses crossing the United States from 1900 to 2050:

(Saros 126, Descending Node) (Saros 143, Ascending Node) (Saros 120, Descending Node) (Saros 124, Descending Node) (Saros 145, Ascending Node) (Saros 126, Descending Node) (Saros 143, Ascending Node) (Saros 145, Ascending Node) (Saros 139, Ascending Node) (Saros 120, Descending Node)
• Solar eclipse of August 21, 2017 (Saros 145, Ascending Node) (Saros 139, Ascending Node) (Saros 136, Descending Node)

Notable annular solar eclipses crossing the United States from 1900 to 2050:

## Boston Total Solar Eclipse History From 1932

Are you excited about the total solar eclipse today? I am! Unfortunately I don’t have glasses, but I’m hoping to enjoy the event anyway.

Also, today I learned that my family has eclipse history. Who knew?

My aunt found a clipping from her aunt’s scrapbook with a portion of a poem called “The Total Eclipse Of The Sun Of Two Centuries Ago.”

I found the full poem online called, “On The Eclipse Of The Sun, April 1715.” It was written by Allan Ramsay, who was born in Scotland in 1686 and died in 1758. With a quick search, I found that the eclipse was on April 22, 1715.

However, with some further digging it seems that because of changes with the calendar that the date of this total solar eclipse, called Halley’s Eclipse, may have actually been on May 3, 1715. Below is portion of the article from The Guardian.

[A] total solar eclipse was visible across a broad band of England. It was the first to be predicted on the basis of the Newtonian theory of universal gravitation, its path mapped clearly and advertised widely in advance. Visible in locations such as London and Cambridge, both astronomical experts and the public were able to see the phenomena and be impressed by the predictive power of the new astronomy.

So this 1715 eclipse was special. It was predicted based on recent scientific developments and the public was ready and waiting to see the spectacular sight. Ramsay, who was about 29 years old at the time, must have been deeply moved by the eclipse, because his poem is quite epic.

Below is a portion, edited for length. See the full poem here.

Now do I press among the learned throng,
To tell a great eclipse in little song.
At me nor scheme nor demonstration ask,
That is our Gregory’s or fam’d Halley’s task
‘Tis they who are conversant with each star,
We know how planets planets’ rays debar

When night’s pale queen, in her oft changed way,
Will intercept in direct line his ray,
And make black night usurp the throne of day.
The curious will attend that hour with care,
And wish no clouds may hover in the air,
To dark the medium, and obstruct from sight
The gradual motion and decay of light
Whilst thoughtless fools will view the water-pail,
To see which of the planets will prevail
For then they think the sun and moon make war,
Thus nurses’ tales oft-times the judgment mar.
When this strange darkness overshades the plains …

What’s especially fascinating about the clipping of this poem, besides the coffee stains, is that my great aunt wrote on it. She wrote that on August 31,1932, she and two of her sisters stood together on Tremont Street in downtown Boston at St. Paul’s Cathedral across from the Park Street T station to view the eclipse.

I’m assuming that they had glasses, because none of them lost their vision from what I know. This story is new to me and gives me some insight into my great aunts’ lives that I didn’t have before. They were really into the eclipse!

Also, my mother pointed out that the names mentioned did not include my grandmother. So now I wonder. Where was my grandmother? And why wasn’t she with her sisters?

As someone who is very much into the idea of time travel, this also makes me think about how I have an approximate time, date and place to go back to to meet some family members!

An article from Science Magazine says that the 1932 total solar eclipse was a path about 100 miles wide that included New England, so they had the real deal, unlike what we will have here in New England later today.

The picture above is from a short video that I found showing the preparation for and actual video from the 1932 eclipse. Today will be full of wonder and no doubt will be history for those looking back at this someday.

## Greek life

Enter the Greeks. For thinkers like Aristotle and others, it wasn’t enough to know that something was happening. It was equally as important to know why it was occurring. “The Greeks became very interested in causation,” Seitz says. The meaning of the eclipse was less important than other factors: “For them, you don’t understand something until you can explain it.”

Greek observations helped figure out how planets move and that the shape of the Earth is a sphere. Without telescopes, they still thought of the moon as a luminous heavenly body, vastly different from our rocky home, but they figured out its relative motion compared to Earth. And even though they thought that the Earth was the center of the Universe, they figured out that an eclipse is the shadow of a new Moon cast by the sun onto the Earth.

Techniques developed by Aristotle and Ptolemy to understand eclipses were in use all the way up until Copernicus and Newton stepped on the scene hundreds of years later.

“That’s not to say that nothing happened in the intervening time,” Seitz adds. People kept building on ancient cultures’ knowledge, accumulating more data, and starting to refine techniques during the Middle Ages. “In the Islamic world in particular, they paid a lot of attention to astronomy and astrology, developed astrolabes to take angles in the heavens, and tried to refine the system,” Seitz says.

Later, thinkers like Tycho Brahe built giant quadrants to make more accurate measurements of the movement of the Sun during eclipses, and some people used techniques to measure the eclipse that we still use today. “They did use pinhole cameras in the medieval period, which lets you measure the magnitude of the eclipse a little better,” Seitz says.

Europe was far from the only place to notice that eclipses were happening. China developed their own eclipse predictions at around the same time as people in the Mediterranean, paralleling the discovery of the patterns of eclipses thanks to their long history of record-keeping. There is evidence that the Mayans also had ways of measuring eclipses, but virtually all their records were brutally destroyed by conquistadors during the European invasion of the Americas.

Despite greater understanding of eclipses, most cultures still saw them as bad omens. Interpretations (slowly) started to change with the advent of telescopes, which revealed the topography of the Moon and allowed eclipse predictions to get much more precise. In fact, in the 1700’s astronomer Edmond Halley made a map of the path of the coming eclipse and published it in the hopes that the general public wouldn’t panic when the Sun briefly disappeared, and that observers might gather more data on how long the eclipse lasted at different locations. The modern era of eclipse observing had finally begun.

## The Solar Eclipse Is Coming. But How Do We Know, And When Did We Know It?

On Aug. 21, most North Americans will see at least a partial solar eclipse. But people in 12 states — in a 70-mile-wide swath from Oregon to South Carolina — will experience a total eclipse. The schedule is known with precision, but how do we know all this and when did we first know it?

Here & Now‘s Meghna Chakrabarti talks with Sky & Telescope magazine’s Kelly Beatty ( @NightSkyGuy) about the science of the eclipse.

#### Interview Highlights

On how our knowledge of the August total solar eclipse is so precise

“There’s a giant clock going on in our solar system. The moon goes around the Earth, the Earth goes around the sun, we know those periods very precisely. Eclipses of the sun can be predicted thousands of years in advance. In fact, we’ve known about this eclipse, and it’s been on all of our calendars for decades now. This is the first total solar eclipse to cross the continental U.S. since 1979, first one to go coast-to-coast since 1918 — that’s 99 years ago. And yes, we do know with that much precision.”

On whether there’s any uncertainty about the eclipse’s path

“There really isn’t any uncertainty. I am going to be at a place in [Hopkinsville, Kentucky], where I can predict when the sun will disappear behind the moon, and when it will reappear to the nearest tenth of a second. And the reason for that has to do with — it’s cliche — but it’s space-age precision. We now know the motions of the planets far better than we used to be able to. Because if you think about it, you look up at the moon in the sky and you say, ‘Well, where is it gonna be? How fast is it moving?’ Now we have spacecraft that are around and on the moon, and the precision of our radio transmitters and tracking is far more accurate than just watching the moon cross the sky.”

On how our understanding of the moon has developed over time

“There was a time — and it wasn’t that long ago, five or 10 years ago — when the basic eclipse predictions assumed that the moon was a perfect circle in the sky, and that the sun was a perfect circle in the sky. And so the computations were done on that basis. But we know, because our spacecraft have shown us, with incredible detail the highs and lows of the moon — we’ve mapped every mile of that place. That the moon is an irregular body, and especially along the edge, along the outer rim during an eclipse, there are going to be mountains and valleys, and so depending on where the sun disappears from where you are, maybe it disappears behind a mountain, in which case the eclipse starts early for you. Or maybe it disappears in a valley on the moon, and it lingers a little bit longer and so the eclipse is gonna start late for you. We can now predict all of that well in advance.”

On humans predicting eclipses thousands of years ago

“It turns out — here’s your word for the day: Saros — that the geometry of the Sun and Earth and Moon repeats with a period of 18 years, 11 days and eight hours, almost exactly. So on Aug. 10 in 1999, there was a total eclipse of the sun. It had almost exactly the same path, almost exactly the same duration, in the same latitudes on the Earth. But because of that eight-hour difference, it didn’t take place over the U.S., it took place over Europe. And so that Saros, that notion of that periodicity, that long-range periodicity, has been known since ancient times. And if you think about it, three Saros cycles, the eight hours add up and so every 54 years, a total eclipse of the sun happens about in the same place as it did 50 years before. The Babylonians and Assyrians knew this as early as 200 or 300 B.C. And so we’ve they’ve been able to tell us that eclipses were coming for that long. It’s remarkable that they had the wherewithal to figure that out.”

On where to buy non-counterfeit eclipse glasses

“Up until about two weeks ago we were saying, look for something called an ISO certification, which would be stamped on the back. But guess what? That can be counterfeited too. If you go to the website of the American Astronomical Society, there is a list of approved — not just vendors, manufacturers — but the vendors, the places to go where you can be assured that you’re getting quality glasses. And they’re widely available. So I guess my suggestion is, don’t order them over the internet. Go to a brick-and-mortar store.”

## Ancient Irish Were the First Known to Mark an Eclipse in Stone

More than 5,000 years ago people in Ireland carved a representation of an eclipse into three stones at a megalithic monument—the first known recording of a solar eclipse, scholars say. Researchers have further noted that the sun shines into a chamber of this monument in County Meath on the later ancient Celtic festivals of Samhain and Imbolc.

Our ancient Irish ancestors carved images of an ancient eclipse into giant stones over 5,000 years ago, on November 30, 3340 BC to be exact. This is the oldest known recorded solar eclipse in history. The illustrations are found on the Stone Age “Cairn L,” on Carbane West, at Loughcrew, outside Kells, in County Meath. The landscape of rolling hills is littered with Neolithic monuments. Some say that originally there were at least 40 to 50 monuments, but others say the figure was more like 100.

“Cairn L” received a mention in Astronomy Ireland ’s article: “Irish Recorded Oldest Known Eclipse 5355 Years Ago.” They write that the Irish Neolithic astronomer priests recorded the events on three stones relating to the eclipse, as seen from that location.

Researchers Jack Roberts and Martin Brennan found the sun illuminates a chamber in the monuments on November 1 and February 2, the cross-quarter days, which marked dates halfway between solstices and equinoxes.

A solar eclipse, May 20, 2012 (Photo by Brocken Inaglory/ Wikimedia Commons )

November 1 is the end of summer, which is what Samhain means. The ancient Celts, who came later than the people who made the eclipse carving, considered Samhain the beginning of winter. Christians call it All Saints Day.

February 2, or Imbolc, is midway between the winter solstice and the spring equinox. It was later celebrated by Christians as Candlemas and in Ireland as St. Brigit's Day. The Celts called it the Festival of Lights and lit every candle and lamp in the house to commemorate the rebirth of the sun. Christians too celebrated February 2 with lights. On that day candles were lit in churches to celebrate the presentation of Jesus Christ in the Jerusalem temple.

The Irish called it Imbolc (“lamb's milk”) because it was when lambing season started.

“It was also called Brigantia for the Celtic female deity of light, calling attention to the Sun's being halfway on its advance from the winter solstice to the spring equinox,” Alamanac.com explains.

Angels take St. Bride or Brigit, a Catholicized ancient Celtic goddess of light, to Bethlehem to foster the Christ child, John Duncan ( Sofi/Flickr)

Imbolc is also called Brigit's Day. Brigit means The Bright One. This sun goddess, later subsumed into the Catholic roster of saints, presided over the forge and hearth, crops, livestock and nature and also inspired skills of sacred arts and crafts, according to Celticatlanta.com.

Irish Central reports that many people believe the Celts invented the Festival of Lights to welcome the eclipse. They are also believed to have predicted when the eclipse would happen.

Brennan and Roberts noted the sun may not have shown into the chamber on Samhain and Imbolc when the Celts built it in 3340 BC.

In addition, Brennan and Roberts observed full moonlight illuminating the end of the cairn, where light shone on a cup mark on the endstone on August 26, 1980. Then, as the light moved across the chamber, it illuminated the bottom of the Whispering Stone.

“The 3340 BC eclipse is the only eclipse that fits out of the 92 solar eclipses in history tracked by Irish archaeoastronomer expert, Paul Griffin,” Irish Central says. “With none of the technology available to our modern experts the ancient Irish constructed these complex structures, that not only endured over 5,000 years, but were built with such accuracy that they continue to perform their astronomical functions today.”

Within Cairn L is a tall stone pillar called the Whispering Stone, 2 meters tall (7 feet). Irish Central believes that the chamber and cairn were built to house the Whispering Stone.

Featured image: One of the Loughcrew eclipse rocks ( IrishCentral)

The principle was known long ago, to the Babylonians and Hellenistic Greeks but the accuracy of prediction depends on the detail of the Lunar motion (the motion of the Sun is relatively simple). Without a precise Lunar theory, it was possible to predict that an eclipse is LIKELY to happen on such and such date and time, but not with a 100% certainty, and the place where it will be visible and other features could not be predicted.

Of course there were many cases when an eclipse was predicted and really happened, see, for example http://en.wikipedia.org/wiki/Solar_eclipse_of_August_21,_1560

Another question is how far in advance one could predict. I suppose at the time of Brahe it was possible to predict an eclipse several months in advance.

Let me give an example in 1598 the almanac gave a solar eclipse on March 7 and a lunar eclipse with the error of one hour. This led Kepler to the discovery of the 4-th inequality (see below). An almanac is supposed to make predictions for one year.

Sufficiently precise Lunar theory for accurate predictions for several years in advance, with 100% certainty and where it will be visible, and other features of the eclipse, was developed in the middle of 18 century, as a result of combined efforts of several greatest mathematicians of that time (Clairaut, Euler, T. Mayer).

But there are many records of more or less accurate predictions before that time, beginning from antiquity.

Remark 1. This is very different from the Lunar eclipses which do not require knowledge of fine detail of the Moon motion. Prediction of the Lunar eclipses was possible since antiquity.

Remark 2. The main motivation for these efforts was not the eclipse prediction but more important practical problem: determination of the longitude at sea by the "Method of Lunar distances". But almost at the same time, chronometer was invented, and for about 1/2 of a century the two methods were competing. When chronometers became affordable (in the first half of 19-th century, the method of Lunar distances gradually was displaced by a simpler method, based on a chronometer).

EDIT. Let me elaborate as much as possible without MathJax. First of all, what does it mean to "predict"?

If 10% of the Sun disc area is obscured, is this an eclipse or not? This is what I mean by "features", full or not full, perhaps circular. The same eclipse will be full in one place and partial in another.

Second important question: predict how much in advance? 2 days? 2 months? 2 years? or 1000 years? This makes a great difference.

Now a brief account of what was involved. I assume that the Sun motion is known precisely (it was known to sufficient accuracy to Hipparchus). So we only discuss the Moon. Both Sun and Moon have visible diameter about 1/2 degree. So to predict an eclipse at a given location and time we need to know the Moon motion, say to minutes of angle.

From the time of Hipparchus to this time, the (geocentric) coordinates of the Moon as functions of time are described by a series of the form $At+E(t)+E'(t)+E''(t)+ cdots$ where $t$ is time, $A$ is the "mean motion" and $E$ s are periodic terms depending on the mutual position of Sun and Moon. These periodic terms are called "inequalities". The first inequality is due to Hipparchus and its maximal amplitude is about 6 degrees. Second inequality (a. k. a. evection) was discovered by Ptolemy, its maximal value is 2.5 degrees.

While the first inequality is due to ellipticity of the orbit (Kepler's law, as we know now), the second inequality is due to the influence of the Sun.

There was no much progress between Ptolemy and Tycho, except perhaps that some numerical constants were determined more precisely. Astronomers before Tycho did not measure angles with sufficient precision. Their theories were based on Lunar eclipses, not on the direct angle measurements.

It was Tycho Brahe who discovered the third inequality (a. k. a. variation) which can be as large as 40' (that is greater than the diameter of the sun or of the Moon). Later Kepler and Brahe discovered the forth inequality (of amplitude 11').

At this point the development stopped, because already the second inequality cannot be explained by the Kepler laws (Kepler laws solve the 2 body problem, and here we have 3 bodies: the influence of the Sun is not negligible, as we see already from the second inequality). For example, Jupiter obeys Kepler's laws to very high accuracy, because the influence of other planets is negligible. But Earth-Moon-Sun system is a real 3 body system, and Moon does not obey Kepler's laws with sufficient accuracy.

With Newton's Universal law of gravitation, the first and most important problem was whether it gives anything new besides the Kepler Laws. (After all "explanation of the Kepler Laws was not such a great achievement because the Gravitation Law was derived from these very Kepler laws). The problem was to predict NEW phenomena, or at least (as a first step) to explain the third inequality.

It is known (nowadays) that the three body problem has no closed form solution. This is a system of differential equations based on the law of gravity, but this system cannot be exactly solved. So the major efforts of the best 18 century mathematicians were spent on finding a useful approximate solution. Some of them were stimulated with the practical of this problem which I mentioned above. After the great efforts (the main contributors are Clairaut, Euler and Mayers, but also many others) the theory permitted to compose lunar tables which predicted Moons position for several years in advance with the accuracy to fractions of a minute.

THIS was the decisive test of the law of gravitation. Another test, some times earlier was the correct prediction of the shape of the Earth, confirmed by precise measurements.

Mayers and Euler shared a part of the Longitude Prize given for the solution of the problem of longitude by the British Parliament. (The main part of this prize was awarded to Harrison who invented chronometer at approximately the same time). Nautical Almanac based on Mayers tables was published. It gave predictions for one year. I examined the early issues of the Almanac, and can say that the maximal error in Moon's position was about 0.2'. But every year it had to be corrected. Further mathematical achievements of 19-th century made possible very long term predictions (say, 2000 years) with the accuracy within seconds.

Modern formula contains several THOUSAND periodic terms, "inequalities". So we can easily tell that some eclipse happened on such and such date (say 1545 BC) at such time, when such and such Babylonian king reigned, and the eclipse was 35% at in a given city. This degree of accuracy of "predictions" was only made possible in 20-s century, approximately since 1910.

The previous, very simplified discussion concerns only Moon's motion in longitude. The motion in latitude is even more important for the eclipse prediction, and it is described similarly. The key steps are due to Hipparchus (inclination of the orbit), Brahe (first inequality), Kepler (elliptic orbit), Newton (law of gravity), d'Alembert, Clairaut and Euler (approximate solution of Newton's equations) and Mayer (making of the tables).

I should also mention that at the time of Hipparchus, there existed a different theory, of Babylonian astronomers which had approximately the same accuracy and was based on different mathematics. This theory was practiced as late as 19-th century in India, by Tamil astronomers, and it gave good predictions of Lunar (not Solar!) eclipses.