Comet Lovejoy is a gassy comet with a short tail appearing green proably due to the presence of two gases –
cyanogen (CN)2 and diatomic carbon (C2) – which glow green when their molecules
are ionised. Ionisation causes electrons within the
molecules to gain energy and when the electrons drop back down to their normal
state, they give off light of a certain wavelength. For these molecules they
emit green light and since they are very strong emitters, their green colour
dominates the comet. The evening sky remains free of moonlight
for excellent views until about January 23rd or 24th, when the waxing Moon will
brighten the sky further each night. Lovejoy passed closest by Earth on January
7th, at a distance of 70 million kilometers.
Although the comet is now receding from us, its intrinsic brightness is
still increasing slightly. That's because it doesn't reach its closest to the
Sun, until January 30th although by this date the comet will be fading from
Earth's point of view and the Moon will be brightening. The comet covers 3° per day at its peak, meaning it will move
noticeably in a single observing session. Amateur astronomer Terry Lovejoy
discovered this object on August 17, 2014, from Brisbane, Australia. Comets
that first light up the deep southern sky tend to have orbits inclined steeply
to the solar system’s plane, a characteristic that often carries them well
north after they wheel around the Sun. The below photographs were taken 16
January 2015, in the desert near to Tabuk in north-west Saudi Arabia by Viv
Wilson who has kindly allowed me to use them on my website.
