Why eclipses make good historical anchors
The orbits of the Moon and Earth can be calculated far back in time. When an ancient text mentions that the Sun went dark at a certain place, astronomers can look for a matching eclipse and often find only one candidate. That turns a vague story into a precise date.
Ancient records have also helped science. By comparing where historical eclipses were actually seen with where they would be seen if Earth’s rotation never changed, researchers such as the British astronomer F. Richard Stephenson measured how tidal friction has gradually slowed Earth’s spin, lengthening the day by a tiny amount each century.
763 BC: the Assyrian eclipse
Assyrian records list each year by the name of an official. The entry for one year, under the official Bur-Sagale, notes a solar eclipse in the month of Simanu. Astronomers identify it with the eclipse of June 15, 763 BC, which was total across northern Mesopotamia.
That single line lets historians convert the Assyrian list of years into fixed dates, and through it many other events in the ancient Near East.
585 BC: the eclipse that stopped a battle
The Greek historian Herodotus tells of a war between the Medes and the Lydians in what is now Turkey. In its sixth year, during a battle, day suddenly turned to night. Both armies stopped fighting and soon made peace.
Herodotus adds that the philosopher Thales of Miletus had predicted the eclipse. Modern calculations identify it with the total eclipse of May 28, 585 BC, making it one of the earliest events in Greek history with a precise date.
1715: Halley maps the shadow
Before the total eclipse of 1715 crossed England, the astronomer Edmond Halley published a map showing the predicted path of totality across the country. He asked observers to report what they saw, so that he could check his predictions. The eclipse came on April 22 by the Julian calendar England then used, May 3 in the Gregorian calendar. His forecast was close, off by only a few minutes in time, and his map set the style for eclipse maps used ever since.
1860 and 1868: the Sun’s atmosphere and a new element
During the total eclipse of July 18, 1860 in Spain, photographs taken from different sites helped show that the glowing prominences seen around the Moon belong to the Sun, not the Moon.
During the total eclipse of August 18, 1868, the French astronomer Jules Janssen, observing from India, studied the light of those prominences with a spectroscope. A bright yellow line appeared that did not match any known element. The English astronomer Norman Lockyer concluded that it came from a new element, which he named helium after the Greek word for the Sun. Helium was not found on Earth until 1895.
1919: Eddington tests Einstein
Albert Einstein’s general theory of relativity predicted that the Sun’s gravity should bend the light of stars passing close to it, by twice the amount older theory suggested. Normally the Sun’s glare hides those stars, but a total eclipse makes them visible.
For the total eclipse of May 29, 1919, British teams traveled to the island of Príncipe off West Africa, led by Arthur Eddington, and to Sobral in Brazil. They photographed stars near the eclipsed Sun and compared their positions with photographs taken at night. The results, announced in November 1919, supported Einstein’s prediction and made him world famous.
Modern shared eclipses
Recent eclipses have become mass events. The total eclipse of August 11, 1999 crossed Europe and parts of Asia. On August 21, 2017, a total eclipse crossed the United States from coast to coast, and on April 8, 2024, another passed over Mexico, the United States and Canada. Each was watched by millions, many with eclipse glasses, as explained in the guide to solar eclipse eye safety.
Old fears and stories about eclipses are collected in solar eclipse myths. For future events, see the eclipses page, and for the basics, read what a solar eclipse is.