Solar eclipse at Palm Cove, Australia, 2012.  (Credit: Ian Hitchcock/Getty Images)
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Introduction

Solar and lunar eclipses—astronomical events that occur when the Earth, the Sun and the Moon are aligned—have figured prominently in human history. Striking to behold, eclipses often were viewed as supernatural phenomena. They also allowed ancient civilizations to develop sophisticated calendars, convinced Aristotle the Earth was round and helped Einstein prove his theory of relativity.

A solar eclipse happens when the Moon passes between the Earth and the Sun and partially or fully blocks the view of the Sun. When the Moon passes directly behind the Earth, into its shadow, a lunar eclipse occurs.

A total solar eclipse happens when the Moon totally covers the Sun’s disk. During a total solar eclipse, the daytime sky may darken briefly and the temperature may drop. A total solar eclipse may last only a few minutes. They are rare events at any given location, because the Moon’s shadow is small relative to the size of the Earth and traces a narrow path across Earth’s surface.

During a total lunar eclipse, the Moon turns a reddish color, because the only light seen is refracted through the Earth’s shadow. Total lunar eclipses are sometimes called blood moons.

November 30, 3340 B.C.: A series of circular and spiral-shaped petroglyphs at the Loughcrew Megalithic Monument in County Meath, Ireland, are believed to correspond to a total solar eclipse visible in the region on that date. The discovery of charred human bones beneath a stone basin inside the monument only adds to the mystery of this site.

October 22, 2134 B.C.: One of the earliest solar eclipse records appears in the Shu Ching, an ancient Chinese book of documents. The ancient Chinese believed that a solar eclipse was the result of a large dragon eating the Sun. It was the job of two royal astronomers named Hsi and Ho to predict such events so that people could prepare bows and arrows to fend off the dragon. However, they shirked their duties in order to get drunk and were beheaded by the emperor as a result.

May 28, 585 B.C.: According to the ancient Greek historian Herodotus, a total solar eclipse brought about an unexpected ceasefire between two warring nations, the Lydians and the Medes, who had been fighting for control of Anatolia (modern-day Turkey) for five years. During the Battle of Halys, also known as the Battle of the Eclipse, the sky suddenly turned dark as the sun disappeared behind the moon. Interpreting the inexplicable phenomenon as a sign that the gods wanted the conflict to end, the soldiers put down their weapons and negotiated a truce.

August 27, 413 B.C.: At the height of the Peloponnesian War, a decades-long struggle between Athens and Sparta, Athenian soldiers found themselves locked in a losing battle to expel the Syracusians from Sicily. Their commander, Nicias, ordered a temporary retreat.

As the troops prepared to sail home, however, a lunar eclipse took place, prompting the highly superstitious Nicias to postpone the departure. The Syracusians took advantage of the delay to stage another attack, overcoming the Athenians and weakening their stronghold on the Mediterranean. According to many historians, the defeat in Sicily marked the beginning of the end of Athenian dominance.

29-32 A.D.: Christian gospels say the sky darkened after the crucifixion of Jesus. Some accounts suggest the event may have coincided with a solar eclipse. Historians have used astronomical records of solar eclipses in the years 29 C.E. or 32 C.E. to try to pinpoint the death of Jesus.

May 5, 840: The third son of Charlemagne, Louis the Pious inherited a vast empire in what is now modern-day France when his father died in 814. His reign was marked by dynastic crises and fierce rivalry between his sons. A deeply religious man who earned his nickname by performing penance for his sins, Louis reportedly became terrified of an impending punishment from God after witnessing a solar eclipse. According to legend, he died of fright shortly thereafter, plunging his fractured kingdom into a civil war that didn’t end until the historic Treaty of Verdun in 843.

February 29, 1504: Twelve years after his momentous landing at San Salvador, Christopher Columbus was exploring the Central American coast when woodworms attacked his ship, causing leaks and forcing him to make an emergency stop in Jamaica. He and his crew spent more than a year there awaiting relief. The indigenous people of the island welcomed the men, offering them food and shelter, but cut off their supplies when some of Columbus’ crew members began stealing from them.

Hoping to impress his hosts and regain their support, Columbus consulted the almanac he had brought with him and read about an upcoming total lunar eclipse. He told the Jamaicans that the gods were unhappy with them for failing to provide assistance and that they would show their disapproval by turning the moon a bloody red color. The eclipse occurred on schedule, and the astonished Jamaicans promised to resume feeding Columbus and his crew.

Scientists have studied eclipses since ancient times. Aristotle observed that the Earth’s shadow has a circular shape as it moves across the moon. He posited that this must mean the Earth was round.

Another Greek astronomer named Aristarchus used a lunar eclipse to estimate the distance of the Moon and Sun from Earth. The Moon’s ability to cover the Sun’s disc during a total solar eclipse also allowed the ancient Greeks to describe the Sun’s corona—the aura of light that surrounds the Sun.

Scientists have used eclipses to make discoveries in more recent times, too. On May 29, 1919, Sir Arthur Eddington tested Albert Einstein’s theory of general relativity during a total solar eclipse. Einstein had theorized that massive objects caused distortions in space and time. Eddington confirmed that starlight bent around the sun by measuring the position of certain stars relative to the eclipse.

On August 21, 2017, a total solar eclipse will cross the United States from coast to coast. Viewers in the direct path of the eclipse will experience a total solar eclipse, while people outside the direct path will see a partial eclipse.

Looking directly at the sun without eye protection during a solar eclipse can cause eye damage. However, there are ways to safely view a solar eclipse.

DIY pinhole “cameras” allow viewers to track the progress of the Moon’s across a projection of the Sun’s surface, while special solar-viewing or eclipse glasses make it safe for the wearer to stare directly at the Sun.

SOURCES

Eclipse History. NASA.
The Long History of the Lunar Eclipse. NPR.
May 29, 1919: A Major Eclipse, Relatively Speaking. WIRED.
The 8 Most Famous Solar Eclipses in History. LiveScience.com.