The facts about the “Green Comet”

At the start of January I asked some MBO members if they had heard about a comet in the media. They all shook their heads at me. Several weeks later you can’t seem to open your social media pages without every media outlet shouting “See the once-in-a-lifetime rare green comet!” at you. Oh dear. And its not even visible from Australia yet! Let’s get some facts straight about it to get you prepared.

What is this comet called?

It’s called C/2022 E3 (ZTF), which doesn’t exactly roll off the tongue. The “C” is for Comet and tells us it is a comet seen for the first time. 2022 is the year it was discovered, “ E” tells us it was discovered in the first half of March 2022, and the “3” tells us that it was the third comet in the first half of March 2022 to be found. The ZTF is the discoverer, which in this case is the Zwicky Transient Facility, which is a wide-field sky astronomical survey based at Palomar Observatory in California, USA.

Is it really rare?

Not really. Comets often exhibit this characteristic green colour in photographs. Some comets are more green than others, and that is no surprise, some variation is expected. What you shouldn’t expect is to see this colour with your own eyes. It likely will not be intense enough for your human eyes to pick up even if viewed through a telescope.

Why is this comet green?

The green colour seen in photographs comes from molecule called dicarbon (that’s two carbon atoms together) breaking apart. Not something that is common on relatively warm Earth by itself because it breaks down too quickly, in the cold depths of space away from the Sun it has time to cluster around the coma as it is released as carbon chloride from the ice and dust on the nucleus of the comet, stripped of the associated chlorine atoms by ultraviolet light from the Sun, then split apart by the solar wind.

But it is the first time has been seen in 50,000 years!

Yes, but a proportion of comets we see each year are what are known as “long period comets,” which are comets that seen for the first time, or the first time in recorded human history. They may be on their early stages of becoming a short period comet, as they haven’t had a close encounter with Jupiter or Saturn that has bent their orbit significantly to make it shorter.

Where can I see it?

If you are in southern Australia, this comet wont be visible to you until the 5th February 2023 or later, as before then it will below your northern horizon. It will quickly move up through Auriga to Taurus, and will be near the planet Mars on the 11th and 12th of February. On the 15th it will be near the bright start Aldebaran in Taurus. After that it keeps travelling up (southward), but its rate will slow, and the comet will likely fade as it moves away from the Earth and the Sun. Perihelion, when it was at its closest point to the Sun in it orbit, and therefore at its most active, was on 12thJanuary 2023, and closest point to Earth is 1st February 2023.

The Full Moon for February is on the 6th, which means it will flooding the sky with light all night, and will make the much fainter and low to the horizon comet difficult to see. From the 7th onwards, there will be a larger window each evening to spot the comet before the Moon rises, plus the comet will be a little higher above the northern horizon.

How can I see it?

Try using binoculars to spot the fuzzy blob that marks the nucleus of the comet. Once you know the location for the night, give yourself some time to become dark-adapted, letting your irises open to their maximum and see if you can detect the broad fan of the dust tail, which is mostly pointing away from us.

If you have a telescope you can try as well, but use a low magnification. If you use too high a power you may look straight through the comet!

The final word should always be about the unpredictability of the behaviour of comets. We know the orbit they will travel, but we don’t always know they will present to us. As the well-known comet observer David Levy once said “Comets are like cats – they have tails and do what they want to do.” And that is why its always worth attempting to have a look, no matter what the facts of a comet are.

Links to maps:

Southern Comets Homepage and choose Comets from the menu on the left.

Jacquie Milner

MBO Director of Astronomy

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