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People have been studying total solar eclipses for thousands of years to better understand the cosmos.
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Total eclipses helped create Einstein’s theory of relativity and led to the discovery of helium.
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Here are seven instances where total solar eclipses have helped advance our understanding of science.
On April 8, millions of people across the US will do the same thing: look up.
In mid-afternoon, day will turn to night, as a total solar eclipse touches 15 states.
We now know what causes a total solar eclipse. But our ancient ancestors from thousands of years ago were not so sure, and that was bad news for some scientists.
In the 21st century BCE, two astronomers were reportedly deposed by the emperor of China for not predicting a total eclipse.
Over the centuries, total eclipses became less of that and more of an opportunity to test scientific theories and create new discoveries.
Here are seven times a total solar eclipse helped advance human science.
1. Measuring the Earth’s Rotation
Some of the earliest suspected eclipse records go back thousands of years.
Some experts have suggested that petroglyphs or rock carvings found on a monument in Ireland refer to an eclipse that occurred on November 30 in the year 3,340 BCE. Others have expressed doubts.
Human-made markings on turtle shells from China and Babylonian tablets dating back more than 3,000 years may contain ancient references to eclipses.
Although these records can be interpreted, scholars have studied historical descriptions of eclipses for centuries. This is how the 18th century astronomer Edmond Halley first realized that the Earth’s rotation had slowed down over thousands of years.
2. Find out what causes the eclipses
Two modern scholars credit the Greek philosopher Anaxagoras of Clazomenae with demonstrating the role of the moon in eclipses, calling him “perhaps the first empirical astronomer.”
He probably developed his theories after seeing an annular eclipse, or “ring of fire,” on February 17, 478 BCE. Although he got some of the science right, his complete understanding of the solar system was a product of his time.
Anaxagoras, for example, thought that the pressure of the air held the Earth flat in the center of the rotating sun, moon and stars. Despite that error, he worked out the basic mechanisms behind eclipses.
Anaxagoras correctly believed that the moon reflected the light of the sun. He was also accurate in his theories that when the moon moved in front of the sun, it caused a solar eclipse. Similarly, when the Earth would be between the sun and the moon, there would be a lunar eclipse.
He also used the moon’s shadow during an eclipse to estimate its size, but his calculations gave him a much smaller answer than it actually was.
3. To estimate the distance of the moon from the Earth
On March 14, 189 BCE, a total solar eclipse swept over what is now northern Turkey. The Greek astronomer Hipparchus was only a child at the time, but he may have seen the event.
Years later, Hipparchus may have used second-hand accounts of that same eclipse to make one of the most mathematically accurate estimates of the age of the moon’s distance from Earth.
Although the exact writings of Hipparchus have been lost, a 4th century scholar described how he used the knowledge.
The astronomer measured the distance between where the total eclipse was in modern-day Turkey and Alexandria, Egypt – where a fifth of the sun appeared – to make his calculation.
Based on his mathematics, Hipparchus offered several ranges, including an average distance of about 281,387 miles.
It wasn’t terribly far from it. The moon is about 238,855 miles away.
4. Predicting the path of an eclipse
In the 11th or 12th century, Mayan astronomers made an amazing prediction of their time: They calculated that a total solar eclipse would occur in 1991, and their prediction was accurate to within a day.
It would be hundreds of years until people made more accurate predictions. In the 18th century, Edmond Halley, better known for a comet bearing his name, made a map predicting the path of the solar eclipse on May 3, 1715 with great accuracy.
Others made maps before him, but Halley based his predictions on Isaac Newton’s theory of universal gravitation, which helped him time the eclipse to within four minutes.
5. Discovery of helium
Helium is very abundant in the universe but rare on earth. It took an eclipse for an astronomer to find out.
French astronomer Pierre Jules César Janssen traveled to Guntur, India just for the eclipse of August 18, 1868. He was using a spectroscope, a prism-like device for separating sunlight into a spectrum.
Janssen saw a yellow line with a wavelength unlike any other element. Around the same time, the English astronomer Norman Lockyer developed an instrument to see the sun even without an eclipse. He saw the same line.
Lockyer called the mysterious element helium. It took several decades for scientists to see it on Earth, during experiments on Mount Vesuvius lava and uranium.
6. Proof of Einstein’s theory of relativity
Astronomer James Craig Watson was convinced that he had found proof of a new planet during the eclipse of 1878. Thought to be located between the Sun and Mercury, Vulcan was only visible when the moon blocked the giant star.
Several more eclipses were passed without anyone finding evidence of Vulcan. In 1915, Albert Einstein explained Mercury’s unusual orbit with his general theory of relativity. It would fit the data better than a mysterious, hard-to-spot extra planet.
Despite this evidence, Einstein’s theory did not receive scientific proof until the May 29, 1919 eclipse. The physicist said that the sun’s gravity would bend light from nearby stars.
In 1919, expeditions traveled to Principe, an island off the coast of Africa, and to Brazil. Although the moon blocked the sun, the astronomers took photographs.
The actual stars appeared to have shifted compared to the reference photos. The new apparent locations showed that the sun was bending light within the measurements predicted by Einstein.
7. Studying eclipses from space
Gemini 12 astronauts Jim Lovell and Buzz Aldrin were the first people to see a total eclipse from space. The eclipse moved November 12, 1966 from Peru to Brazil, and the astronauts hovered near the path of totality.
It was a coincidence that they were close enough to see it, according to Smithsonian Magazine. Aldrin’s photos were out of focus and a little disappointing.
Four years later, television networks broadcast an “eclipse of the century,” replete with images of the event. NASA also launched more than two dozen rockets to study UV radiation and solar X-rays during this phenomenon.
The agency still uses rockets to collect data during eclipses and will launch three on April 8.
Read the original article on Business Insider
