Scientific Breakthroughs made during Eclipses

Historical eclipses are still useful today, as they assist scientists study the form and motion of Earth. And even during the upcoming eclipse on June 21, researchers hope to gather valuable data. Atmospheric scientists could also be ready to learn more about gravity waves, ripples in Earth’s atmosphere caused by the moon’s shadow cooling the air in its path (not to be confused with gravitational waves, which are caused by two massive objects like black holes spinning past each other). Still need some proofs? Go through this section to what scientific discoveries and experiments have been performed during eclipses...

 “Discovering” the Sun’s atmosphere

The first reference of the Sun’s corona during a Total Solar Eclipse was probably by Lucien in 932 BCE "… a kind of light is visible about the rim which keeps the shadow [of the moon] from being profound and absolute." Amazingly, the most accurate sketches of corona is credited to May 25, 1751 eclipse, drawn by Cambridge Professor Roger Cotes from England. However, the term ‘Corona’ was coined by the Spanish astronomer José Joaquin de Ferrer, during the June 16, 1806 eclipse, to describe the ephemeral glow of light surrounding the eclipsed sun disk. This led him to the idea that the corona must belong to the Sun, not the Moon, because of its great size.

Interpreting “Solar Cycles”

Around the same time, Samuel Heinrich Schwabe discovered that the number of sunspots countable on the solar surface increased and decreased with a roughly 11-year cycle. This had led astronomers in wondering whether the shape and character of the solar corona also changed with such a cadence. French astronomer Pierre Jules César Janssen was one of the first to recognize this correlation as he compared the eclipses of 1871 and 1878: At sunspot maximum, the corona is rounder; at sunspot minimum, the corona is more elliptical.

Changing shapes of “Corona”

Researches from data obtained during solar eclipses have led to many discoveries later also as the scientists across the world keep on analysing them. Similar studies related to coronal shapes and their changes from one cycle to the next are credited to Russian astronomer Alexi Ganskiy in 1897 and later in 1902 with Indian astronomer Kavasji Naegamvala. The research by Russian solar astronomer A. G. Tlatov at the Central Astronomical Observatory in Pulkovo in 1989 used drawings and photos of all eclipses since 1870 to quantify how the shape of the corona changed from sunspot cycle 12 to 24. There were, indeed, changes that spanned many sunspot cycles suggesting a 100-year cadence for large-scale coronal changes.

 

Coronal shape changes 1870 to 2004Figure 3 – Coronal shape changes 1870 to 2004 (Credit Tlatov: Astronomy &Astrophysics, 2010)

Detecting coronium, the fake element

Such discoveries spanned a nearly 100-year period from the mid-1800s to the 1900’s as technology and our understanding of physics improved. During the eclipse of 1879, Charles Young and William Harkness used a spectroscope to independently discover a new element the spectrum of the Sun's corona: Coronium. Sixty years later, Bengt Edlin deduced that coronium was actually just the element iron seen under very high temperatures having lost 13 of its 26 electrons by the process of ionization. It would take temperatures near a million degrees Celsius to make iron atoms behave this way, which itself was a confounding discovery not to be explained until the late-1900s.

 

Puzzle of Sun’s Temperature: Solution was Sun’s Magnetism

Meanwhile, astronomers continued to scratch their heads over the puzzle of how a star with a surface temperature of 6,000 Celsius could have an overlying corona with a temperature of several million Celsius! With the surprising correlation came the solution!!! The explanation for this mysterious heating also accounted for the shape of the corona itself: magnetism!

Astronomer Frank Bigelow had already noted in 1889 that the coronal streamers observed during the 1878 eclipse had a strong resemblance to magnetic lines of force, so he proposed the Sun must, in fact, be a large magnet. But there was as yet no way to measure magnetism on the sun. This changed in 1908 when George Ellery Hale discovered a way to at least detect the intense levels of magnetism in sunspots. Although Hale’s instruments could not detect the extremely weak magnetic fields in the corona, it was already known by then that the shape of the corona changed with the sunspot cycle, so there had to be some magnetic connection between sunspots and the corona.

 

Estimating the distance from Earth to the moon

Measuring the distance between celestial bodies was not a piece of cake in the past. Astronomers have tried answering that question since 4 centuries before the Christian era , starting with Aristarchus of Samos. Around 150 B.C.E., Greek astronomer, Hipparchus of Nicaea, came up together with his own calculation—using a eclipse. He learned that in north-western Turkey one could see the moon perfectly aligning with the sun. But in Alexandria, Egypt, about 1000 kilometres away, only about 80% of the sun was blocked. Using this information and a few simple trigonometries, he calculated the space between Earth and therefore the moon. And the calculations were quite accurate! It has been known since ancients times that a complete eclipse lasts at the most only a couple of minutes. Thus, the angular size of the Sun is sort of like the angular size of the Moon. It’s relatively easy to measure the angular size of the Moon in the dark.

 

Discovering the new element helium

Up until the 1930s, when scientists developed telescope attachments that block out sunlight, it had been possible to watch the sun’s outer atmosphere only during a eclipse , when the moon passing ahead of the sun blocked its glaring light out. By watching the sun’s atmosphere with a spectroscope, an instrument that separates white light into a good spectrum of colours, French astronomer Pierre Jules César Janssen in 1868 saw an unknown line within the yellow a part of the sun spectrum, which was later found to be produced by a replacement element, now referred to as helium.

On August 18, 1868, Janssen managed to try to do just that. He became the primary person to watch helium, a component never before seen on Earth, within the solar spectrum. At the time, though, Janssen didn’t know what he’d seen—just that it had been something new.

 

Confirming Einstein’s theory of general relativity

Laws in Physics are establsied only with experiments confirming them. Einstein’s Theory of relativity was no exception. The experiment that proves this was also performed during an Eclipse. To check Einstein’s prediction, U.K. astrophysicist Arthur Eddington took pictures of a cluster of stars within the region round the sun, which were visible because of the darkness created by the eclipse. Eddington’s observations confirmed Einstein’s theory.