Green Comet

Skies in the Northern Hemisphere have been graced by a rare, green comet. Now, it's our turn to look for it in Australia – but the view will be dimming ...

But the best way to view the comet will be online. Instead of a dim and distant view, our planet has a perfect ringside seat to see the comet at its finest. Go to the site, pan around to the north, and set the clock (at the bottom right) to an hour or two after sunset – then step forward day by day until ‘C/2022 E3 (ZTF)’ is visible above the northern horizon. Work out where it should be, and scan the sky slowly, looking for a fuzzy patch of light. [five or six degrees per day](https://in-the-sky.org/ephemeris.php?ird=1&irs=1&ima=1&iob=1&objtype=3&objpl=Mercury&objtxt=C%2F2022+E3+%28ZTF%29&tz=0&startday=1&startmonth=2&startyear=2023&interval=4&rows=25) for the first ten days of February. Astronomers soon realised it would come relatively close to Earth in January and February this year, just a couple of weeks after its closest approach to the Sun (perihelion, Comet ZTF is a “long period comet”, which means it’s moving on an extremely elongated orbit around the Sun. The last time comet ZTF graced the inner Solar System was around 50,000 years ago. When they approach the Sun and the temperature rises, that icy surface sublimates (changes directly from a solid to a gas). This means the gas gets rid of the energy it absorbs by shining in specific colours. The comet thus becomes shrouded in a fuzzy “coma” of gas and dust. Sadly, despite the hyperbole, you’re unlikely to spot it with the unaided eye – unless you have great eyesight, a dark sky, and know where to look.