Comet Leonard was discovered on January 3 last year by astronomer Gregory J Leonard at the Mount Lemmon Infrared Observatory in Arizona and catalogued as C/2021 AI. Since its discovery, the comet had been fast approaching both the Sun and Earth, at nearly 160,000 miles per hour.
Comet Leonard made its closest approach to Earth on December 12, when it was 21.6 million miles (34.9 million km) from our planet. It later reached its closest point to the sun on January 3, at a distance of 57.2 million miles (92 million km) from our star.The comet is now hurtling out of our Solar System, never to be seen by Earthlings again. McCarthy took the photo on Boxing Day evening and posted it to his Instagram account cosmic_background, the next day.
Once gases are released they are heated by the Sun and emit energy at different wavelengths. Each molecule has its own emission colour or “fingerprint” which allows us to identify them.Comet Leonard has a greenish tail because its icy rock interior heats up the closer it gets to the Sun, first emitting a blue dust, then yellow or white and finally green. When it turns this teal colour, it means the comet is warm, contains lots of cyanide and diatomic carbon and the potential for it to break up is at its highest.