Today’s Cosmobite is by Sam Knox, an astronomy guide at MAAS – Sydney Observatory.

Comets have been in the news a lot this month. We have seen incredible images taken from the surface of comet 67P/Churyumov–Gerasimenko by the incredibly nimble lander Philae and from Rosetta, Philae’s orbital companion. European Southern Observatory (ESA) engineer, Dr Warrick Holmes, visited Sydney Observatory in December 2014 and presented to senior school students an illustrated lecture about the Rosetta Mission and why comets are important to study.

Dr Holmes is an Australian, born in Adelaide, and he has been part of the Rosetta mission from the beginning.

Recently some incredible images of the ferociously green comet 2014/Q2 (Lovejoy) which is fast approaching the inner solar system at about 35-km/s which is just faster than crossing the English channel in one second.

But what is a comet? A comet is like a huge, dirty snow ball that orbits the Sun, but not like the planets. Their orbits are usually far from circular and when they get close to the Sun they spray gas and dust into space creating two or more distinguishable tails. Comets come from either the Kuiper belt, which is just beyond the orbit of Neptune or the Oort Cloud which reaches out from the Sun at 0.8 light years in every direction. These comets can start falling towards the Sun due to a gravitational tug from a large planet or two comets colliding. At this point, the comets will begin their long voyage towards the Sun heating up and ejecting gas and dust as they get close. These comets can take an incredible 6 million years to orbit around the Sun and their death reminds us of the story of Icarus who flew too close to the sun – they ‘melt’ until they disappear.