I recently saw the 2019 annular solar eclipse from Ooty, India and it was amazing. Another annular solar eclipse is coming up tomorrow, on June 21. If you want to familiarize yourself with what a solar eclipse is and its types, The Planetary Society has a great guide.
An interesting note from my experience seeing the annular solar eclipse - During the ring of fire phase, when the Moon obstructed the Sun the most, everything around was still remarkably lit. The Sun is that bright. It was as if the eclipse never occurred and you still couldn't bear seeing the Sun with your naked eyes. That led me to realize that it is dimmer during sunsets and sunrises than during annular solar eclipses!
I’ve compiled this digest of how solar eclipses have been enabling unique science since a long time.
Discovery of Helium
Scientists used the 1868 solar eclipse as an opportunity to study what the Sun is made up of. They were surprised to find an unknown element in it. The same element which we now know to be the second most abundant one in the Universe – Helium! This second element of the periodic table was thus discovered not on Earth but on the Sun! Smithsonian Magazine has a great article on it.
Einstein’s new model of gravity
May 29, 1919 is considered by many to be the most important solar eclipse of the 20th century. For that is when Arthur Eddington set out to test Einstein’s new model of gravity – the General Theory of Relativity. By looking for changes in positions of stars around the Sun during the solar eclipse, Eddington confirmed Einstein’s prediction that the Sun’s gravity indeed bends light from those stars. Elizabeth Landau has a good narrative on the happenings.
There’s also a good movie named Einstein and Eddington documenting the historic events.
The Sun’s atmosphere
Solar eclipses are of great interest to scientists even today. The Sun’s atmosphere, the corona, is only visible from Earth naturally during a total solar eclipse. The temperatures in the corona cross the million degrees Celsius mark, compared to the much cooler 6,000 degrees on the Sun’s surface. People worldwide are trying to find out why.
To that end, NASA funded several science experiments for the total solar eclipse on Aug 21, 2017 to better understand the corona and its structure.
Orbiting the Sun
The problem of why the corona is much hotter than the Sun’s surface is so fundamental that NASA launched the Parker Solar Probe spacecraft on a mission to go right into the corona and study it up close! Here is my article on this mission to touch the Sun!
ESA also launched the Solar Orbiter this year on a similar mission. On the other hand, ISRO is launching Aditya-L1 next year to conduct uninterrupted observations of the Sun and its corona from afar. It will be placed at the first Lagrangian point (L1) between the Sun and Earth, where the dynamic gravitational attraction between these two bodies roughly cancel out.
The L1 point is not a point as much as a small region in space. It has been host to multiple solar weather monitoring and science observation spacecraft in the past, such as SOHO, ACE, WIND, DSCOVR, etc. Aditya-L1’s observations will complement data from the Parker Solar Probe and Solar Orbiter.
If you get an opportunity to see an eclipse, do so! What an amazing Earth we live on that our Moon and our Sun both have similar apparent sizes for all kinds of eclipses to occur. ☀ 🌕 🌍