This year was especially rare in astronomical circles. The rarity of this year comes from one astronomical object, known as a green comet. This comet’s name is C/2022 E3, quite boring in astronomer jargon. This comet only comes around to Earth every 50,000 years. The last time the comet was visible to those on Earth, Homo Sapiens were not the only humans on the planet. It is quite possible that a Neanderthal was able to see the green hue of this particular comet in the night sky. It and its flight path through the solar system were observed in March of 2022 by astronomers at the Zwicky Transient Facility in California.
Before we can understand why some comets are green in hue, it would be helpful to define what a comet actually is. A comet is an astronomical object that is mostly composed of ice and dust. This ice and dust, when met with the power of the sun, is blown away which gives comets their distinctive tails. Many comets come from the far edges of our solar system, where the power of the sun cannot destroy them over time. The green comet, in particular, is thought to have come from the Oort cloud at the far reaches of our solar system.
Why is this particular comet green? The comet is green due to the ultraviolet radiation the sun gives off when it interacts with the diatomic carbon within the comet. Ultraviolet radiation is just another type of radiation on the electromagnetic spectrum. Since it is not in the visible light category, humans cannot see it. Diatomic carbon is just a molecule of carbon that has two carbon atoms. The diatomic carbon atoms are made when more complex carbon substances at the front of the comet are broken down. When the diatomic atoms are excited by the energy transferred by the ultraviolet radiation, it gives off light which is where the green color of the comet comes from. However, the tail of the comet is not green. This is because ultraviolet radiation can cause the diatomic carbon to break apart. Leading to only regular carbon and other substances being in the tail, which means the carbon and other substances do not give off a green light.
While it is too late to see the comet now, since it has already passed Earth, I hope this article inspires you to learn more about astronomy. There is much more to astronomy than planets, asteroids, and comets. There is a whole universe with galaxies and nebulae waiting to be explored. While it may take generations for humans to reside in these locations, today we can take our telescopes into our backyards and look up at the majesty of the stars.