Eclipses fascinate and inspire us. On Monday our daily routines will be interrupted by the passage of the moon directly in front of the sun that we call a solar eclipse. We will have no choice but to want to look up to take in the splendor of this relatively rare event in nature that will happen regardless of the work deadlines which time your next class starts on campus.
A word of caution: please do NOT look at the eclipse directly. One will need ‘eclipse’ glasses to protect from harmful high frequency light from the sun’s outer layers that can destroy our retinas.
Eclipses make for splendid excuses for doing science experiments. The stories are too many to recount here, so let's narrow the discussion to famous experiments in the area of chemistry alone.
For example, 1868 scientist Pierre Janssen viewed an eclipse through a prism. The prism broke up the light into a rainbow of colors called a spectrum which revealed bright emission bands of light which he correcting associated with being produced by the chemical element of hydrogen.
Curiously, he also saw a bright emission band that was yellow in color. This yellow feature turned out to be produced by the element helium, and this experiment marked the identification of the second element of the periodic table. In sum, we discovered helium in the sun before we found it on Earth!
A year later, in 1869, scientists Charles Augustus Young and William Harkness did a similar experiment and this time in addition to hydrogen and helium they found a closely-spaced pair of green emission bands. It was hypothesized that this might be the discovery of yet another new element in the periodic table.
As the only light they we see during an eclipse is from the outer layers of the sun, the chromosphere and the corona, it was decided to name this potential new element “coronium.” This time it would take another 60 years to correctly identify these green emission bands. As it turned out, they were traced not to a new element but to the known element of iron (Fe).
Iron itself was not all unusual in the 1800’s, so why were scientists so slow to identify it? It turns out that the outer layers of the Sun are so hot that they had removed half of the electrons from the iron atoms, thereby giving it spectral characteristics that we were unused to experiencing here on Earth.
Enjoy the eclipse on Monday!