Records of ancient solar eclipse observations date back to around 2,000 B.C. Before astronomical photography, astronomers and talented recorders drew solar details of eclipses. This gave observers only a few minutes to sketch the sun’s corona, before the total eclipse was over – but the results led to tantalizing glimpses of how variable and dynamic that atmosphere was exciting the curiosity of early scientists.
Given the advantages of using solar eclipses to study the solar atmosphere, scientists and engineers in the 20th century built telescopes and spacecraft to mimic their effects. Known as coronagraphs, these kinds of observatories artificially block out the bright light of the sun to reveal the surrounding corona. Today, scientists gather observations from such coronagraphs as the joint European Space Agency and NASA’s Solar and Heliospheric Observatory, or SOHO, as well as NASA's Solar Terrestrial Relations Observatory, or STEREO. For example, these artificial eclipse-makers help us spot and measure giant eruptions on the sun called coronal mass ejections, or CMEs, that hurl solar material out into space.
Solar eclipses have also helped with physics and chemistry research. A total solar eclipse proved Einstein’s theory of general relativity. According to the theory, light from a star should appear to bend as it passes by the edge of the sun. Observations during a total solar eclipse in 1919 – which blocked enough of the sun's light that stars near the sun were visible in the daytime – showed a star’s apparent position in the sky shift due to the sun’s gravitational influence, thus confirming Einstein’s theory.
Additionally, solar eclipse observations led to the discoveries of new and unexpected elements. Spectroscopy measures light emitted, absorbed or scattered by materials. Therefore, examining spectroscopic data can show what materials gave off or blocked incoming light, making it a great tool for exploring materials in distant stars or other planets. Eclipse spectroscopy detected helium in 1868, 25 years before discovery of the element on Earth.
During a solar eclipse in 1879, two scientists independently discovered another new line in the spectrum of the sun’s corona. The data led the scientists to believe they’d discovered a new element. They named the element coronium. Six decades later an astronomer realized coronium lines weren’t unique, but rather they depicted iron at very high temperatures.
"That incredibly hot iron led to an important area of solar science, called the coronal heating problem," said Ryan Milligan a solar scientist at Queen’s University Belfast in Northern Ireland. "The sun's atmosphere is much, much hotter than its surface and scientists are still trying to establish exactly why."
Despite modern technology, eclipses are still vital to observing and understanding the sun. Coronagraphs in space cannot show the inner corona of the sun, locations where scientists believe CME’s are accelerated. These regions are better viewed during a total solar eclipse.
In addition to research, present day eclipses are watched for their interest value. If you're able to see the March 20, 2015, eclipse, remember to never look at the sun with the naked eye, even during an eclipse.