A Total Solar Eclipse: A Remarkable Astronomical Event that Leads to Significant Discoveries.
On April 8, millions of people across the United States had the opportunity to witness a solar eclipse. At noon local time, the sky darkened as a total solar eclipse occurred in 15 states. Over the decades, total solar eclipses have become less mysterious and have served as opportunities to test scientific hypotheses and lead to new discoveries, according to Business Insider. Here are seven total solar eclipse events that have advanced human scientific understanding.
Total solar eclipses provide valuable research opportunities for scientists. (Photo: Sunset Magazine).
1. Measuring the Earth’s Rotation
Some of the earliest records of eclipses date back thousands of years. Some experts believe that carvings on stones at a monument in Ireland describe an eclipse that occurred on November 30, 3340 BC. Human-made marks on turtle shells from China and Babylonian clay tablets from over 3,000 years ago also mention solar eclipses. Through historical descriptions of eclipses, astronomer Edmond Halley in the 18th century first noticed that the Earth’s rotation has been gradually slowing over millennia.
2. Discovering the Cause of Eclipses
Two modern scholars believe that the Greek philosopher Anaxagoras of Clazomenae recognized the role of the Moon in solar eclipses. He likely developed his hypothesis after witnessing a ring-shaped eclipse on February 17, 478 BC.
Anaxagoras theorized that air pressure caused the Earth to float at the center with the Sun, Moon, and stars revolving around it. Despite this error, he discovered the fundamental mechanism behind solar eclipses. Anaxagoras believed that the Moon reflects sunlight. His hypothesis accurately stated that when the Moon moves in front of the Sun, a solar eclipse occurs. Similarly, when the Earth is between the Sun and the Moon, a lunar eclipse takes place. Anaxagoras also used the Moon’s shadow during an eclipse to estimate its size, but his calculations resulted in a figure much smaller than reality.
3. Estimating the Distance from Earth to the Moon
On March 14, 189 BC, a total solar eclipse passed over northern Turkey. Greek astronomer Hipparchus was just a child at the time, but he may have witnessed the event. Years later, Hipparchus could use descriptions from others about that eclipse to create one of the most accurate mathematical estimates of the distance from the Earth to the Moon. Although Hipparchus’s direct records have been lost, a 4th-century scholar detailed how he used the information.
The astronomer estimated the distance between the location of the total eclipse in what is today Turkey and Alexandria, Egypt (where one-fifth of the Sun was exposed) to make his calculations. Based on these calculations, Hipparchus provided several estimates, including the figure of 452,848 km, which is not too far off from the actual distance of 384,400 km.
4. Predicting the Path of Eclipses
In the 11th or 12th century, Maya astronomers made a remarkable prediction for their time. They calculated that a total solar eclipse would occur in 1991, and their prediction was only off by one day. It wasn’t until many centuries later that humanity could make more accurate predictions. In the 18th century, Edmond Halley, known for discovering the comet named after him, created a map predicting the path of the eclipse on March 5, 1715, with extreme accuracy (off by only 4 minutes), based on Isaac Newton’s law of universal gravitation.
5. Discovering Helium
Helium is abundant in the universe but rare on Earth. An eclipse event helped astronomers discover the element. French astronomer Pierre Jules César Janssen traveled to India to observe the eclipse on August 18, 1868. He used a spectroscope to separate sunlight into a spectrum.
Janssen observed a yellow line with a wavelength unlike any other element. At the same time, British astronomer Norman Lockyer developed a device to observe the Sun even without an eclipse. He also saw a similar colored line. Lockyer named the mysterious element helium. It took scientists two decades to see it on Earth, in experiments with lava from Mount Vesuvius and uranium.
6. Proving Einstein’s Theory of Relativity
Astronomer James Craig Watson was convinced he found evidence of a new planet during the eclipse of 1878. Positioned between the Sun and Mercury, Vulcan could only be observed when the Moon obscured the giant star. Several more eclipses passed, but no one found evidence of Vulcan. In 1915, Albert Einstein explained Mercury’s unusual orbit using general relativity. This explanation matched the data better than a mysterious, hard-to-observe planet.
However, Einstein’s theory of relativity lacked scientific evidence until the solar eclipse on May 29, 1919. The physicist stated that the Sun’s gravity bends light from nearby stars. In 1919, several expeditions went to Principe, an island off the coast of Africa, and Brazil. When the Moon obscured the Sun, astronomers took photographs. The stars appeared to shift positions compared to reference images. The new positions showed that the Sun bent light as Einstein predicted.
7. Observing Eclipses from Space
The Gemini 12 crew, including Jim Lovell and Buzz Aldrin, were the first to witness a total solar eclipse from space. On November 12, 1966, the eclipse moved from Peru to Brazil, and the two astronauts flew near the totality. It was a coincidental event. Aldrin’s photographs were somewhat unclear. Four years later, television networks reported on the “eclipse of the century” that occurred on March 7, 1970. NASA also launched over 20 research rockets to study ultraviolet and X-ray radiation from the Sun during the event. They would continue using rockets to collect data about the eclipse on April 8.
