A solar eclipse runs on a handful of numbers. The Moon is about 400 times smaller than the Sun and about 400 times closer, its orbit is tilted by 5 degrees, and its dark shadow is only a couple of hundred kilometres wide when it reaches us. It also drifts 3.8 cm farther away every year. Between them, those figures decide where and how often totality happens, and how long the Earth will keep having it.
The rest of the story belongs to people. An eclipse may have stopped a battle, and others helped discover a new element, put Einstein’s theory to the test and sent a Concorde racing across Africa. Where a fact has more behind it, a link under it leads to the full story.
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The Sun and Moon look the same size by coincidence
The Sun is about 400 times wider than the Moon and about 400 times farther away, so both appear about half a degree across in our sky.
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Total eclipses will eventually stop
The Moon drifts away from the Earth by about 3.8 cm a year. NASA estimates that in roughly 650 million years it will look too small to cover the Sun completely.
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A total eclipse happens somewhere about every 17 months
In the century from 1926 to 2025 we count 72 total solar eclipses, an average of one every 17 months. Most paths cross oceans or remote land, which is why they feel so rare.
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The longest totality of the last century lasted just over seven minutes
It happened on 20 June 1955, with the path crossing Sri Lanka, India, Myanmar, Thailand, Cambodia, Laos, Vietnam, Philippines. The astronomer Jean Meeus calculated that totality can never last longer than about 7 minutes 32 seconds at one spot on the ground, and the 2027 eclipse, at a little over six minutes, is the longest over land this century.
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Concorde stretched totality to 74 minutes
On 30 June 1973, Concorde 001 took off from Las Palmas in the Canary Islands and flew under the Moon’s shadow at twice the speed of sound, keeping a team of astronomers in totality for 74 minutes before landing in Chad.
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Some years have 5 solar eclipses
Every year has at least two solar eclipses. In our catalogue from 1926 to 2035, 1935 has 5, the most possible in one calendar year.
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One path crossed 17 countries
The path of the total eclipse of 20 May 1947 crossed 17 countries, from Chile to Tanzania. By our calculation, no total eclipse between 1926 and 2035 crossed more.
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The 2027 eclipse is the 2009 eclipse coming back
Eclipses repeat every 18 years, 11 days and 8 hours, a cycle called the saros. The total eclipse of 2 August 2027 is the next in the same series as the long eclipse of 22 July 2009 over India and China.
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Cairo is outside the 2027 path
Many travel articles say the 2027 eclipse is total over the pyramids. It is not: Cairo sees a partial eclipse with about 94.7% of the Sun covered, while Luxor, about 500 km to the south, gets 6m 25s of totality.
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The corona is hotter than the Sun’s surface
The visible surface of the Sun is about 5,500°C (9,900°F), but the corona seen during totality is over a million degrees. Why it is so hot is still one of the big open questions in solar physics.
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Helium was found in the Sun before it was found on Earth
A bright yellow line seen in the Sun’s spectrum during the eclipse of 18 August 1868 led to the discovery of helium, named after the Greek word for the Sun. It was isolated on Earth in 1895.
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An eclipse helped prove Einstein right
Star positions photographed during the total eclipse of 29 May 1919, from Príncipe and from Sobral in Brazil, showed starlight bending around the Sun as general relativity predicted. The results were announced on 6 November 1919.
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The first photo of totality took 84 seconds
Johann Julius Friedrich Berkowski made the first successful photograph of a total eclipse on 28 July 1851 in Königsberg, using a daguerreotype exposed for 84 seconds.
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An eclipse may have stopped a war
Herodotus wrote that a battle between the Lydians and the Medes stopped when day suddenly turned to night, and the two sides made peace. The eclipse of 28 May 585 BCE is the usual match, though historians debate the story.
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The longest totality of the last few thousand years lasted 7 minutes 28 seconds
Astronomers have calculated it for 15 June 743 BCE. The eclipse of 16 July 2186 will beat it by about a second, with 7 minutes 29 seconds.
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The Moon’s shadow can travel at 8,000 km/h
According to NASA, the shadow moves at about 1,770 km/h near the equator and up to about 8,000 km/h near the poles, where it strikes the Earth at a shallow angle.
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Any one place waits about 375 years for totality
A total eclipse happens somewhere on Earth roughly every year and a half, but on average a given spot sees one only about once every 375 years.
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The air can cool by 8°C (14°F) in a few minutes
During the total eclipse of 21 June 2001, the temperature in Lusaka, Zambia, fell by about 8°C (14°F). In 2017, Hopkinsville in Kentucky cooled by about 4.4°C (8°F).
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Giraffes galloped during the 2017 eclipse
Researchers at Riverbanks Zoo in South Carolina saw giraffes break into a gallop and Galápagos tortoises start to mate during totality on 21 August 2017.
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The first people to see a total eclipse from space were Gemini 12 astronauts
Jim Lovell and Buzz Aldrin watched the eclipse of 12 November 1966 from orbit. “The eclipse got to us after all,” Lovell radioed, after it had nearly been dropped from the flight plan.
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More than 600 aircraft flew in the path of one eclipse
On 26 February 1979, the last total eclipse in the contiguous United States for 38 years, air traffic controllers counted more than 600 aircraft in the path of the shadow.
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Solar and lunar eclipses come in pairs
Both kinds need the Sun, Earth and Moon to line up near the Moon’s nodes, so a solar eclipse is often followed or preceded by a lunar eclipse about two weeks apart, in the same eclipse season.
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Annular eclipses never get dark
Even at the peak of a ring of fire, the remaining sliver of Sun keeps the sky bright, and you need eclipse glasses throughout. Only totality is safe to view with the naked eye.
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Sources
- NASA, What’s the very last solar eclipse?
- Beckman J. et al., Eclipse flight of Concorde 001, Nature (1973)
- Pierre Léna, 30 juin 1973, le vol éclipse de Concorde 001
- Universe Today, Who discovered helium?
- Royal Society, Observing relativity
- Space.com, First photo of a total solar eclipse
- Biographical Encyclopedia of Astronomers (N. Hetherington), Thales of Miletus
- Live Science, What’s the longest solar eclipse in history?
- NASA Sun-Earth Day, How fast does the Moon’s shadow move?
- Science News Explores, When the Moon throws shade, weather can change
- NC State University, Animal behavior during eclipses
- Astronomy, The first solar eclipse seen from space
- NASA, Astronomy Picture of the Day, Total solar eclipse of 1979 (19 August 2017)
- The Herald (Everett), The 1979 eclipse