Comet C/2022 E3 (ZTF) as seen from Sydney in February 2023. This chart shows the location of the comet in the sky at 9pm AEDT* from Feb 6 to Feb 20. Look due north and use the star Capella, planet Mars and star Aldebaran as a guide for where to aim your binoculars. Image made with Stellarium.

Update, 2023Feb17: Thank you for all your comments. I’m glad you were able to spot this comet. Unfortunately, after its pretty good showing in the northern hemisphere, for us in the south comet ‘ZTF’ turned out to be very faint (Well, for an astronomer it was bright, but I’m sure for most it was faint, particularly given expectations after the media buildup from the northern hemisphere). My first chance to observe it was on Friday Feb 09 and, for me, even with binoculars and from a dark site it was only just visible. But it was nice to see it had moved on by Sunday!

Back in December 2021 we saw comet C/2021 A1 (Leonard) in our southern skies after it made headlines for its appearance in northern skies. In December 2022 and January 2023 another comet – C/2022 E3 (ZTF) – crossed northern skies and now it too is heading south. There are some good images at Sky and Telescope (and good information on the comet) and more images at SpaceWeather.

From Sydney (and similar latitudes across the country) comet ZTF (for short) first climbs above the northern horizon on Feb 04. From Darwin and the north of Australia this happens on Feb 01 and from Hobart and the south it’s Feb 06. But from wherever you are it will be another two or three days before the comet climbs high enough above the horizon to be readily observable.

When can I first see it from Australia?

If you just can’t wait then our first opportunity, I think, will be on Tue Feb 07. Look for the star Capella, in constellation Auriga, the bright star near the horizon and almost due north at 9pm AEDT (* this time is for NSW, please see my note below for other states). With Capella visible through your binoculars scan slowly above and slightly left of the star and comet ZTF should become visible as a pale, white, fuzzy dot. At 9pm the sky will be dark (after sunset), however the full Moon is just rising and brightening the sky. If you don’t see the comet (more likely the further to the south of Australia you are), try again on Feb 08 – at 9pm the Moon hasn’t risen and the comet will be higher above the northern horizon.

What will I see?

With binoculars the comet will look like a fuzzy, out-of-focus star, small, faint and white. It may be slightly non-circular in shape. I predict it may look something like my photo of comet Leonard – but I will update this when I first see it myself!

Don’t expect to see any green colour, no long gossamer tail (the ion tail), nor the comet whizzing past the stars! Colour will require a medium-sized telescope (at least), the full tail will require long-exposure photography and to see motion look again in an hour or two and you may see it has moved against the background stars.

But, what you do see is a kilometre-sized (roughly) ball of dust, rock and vaporising ices (mostly carbon dioxide and water), a remnant from the formation of our Sun and planets four-billion years ago, coming in from far beyond Neptune and now passing Earth on its way out of the solar system altogether – never to return. Or maybe not…this comet has a hyperbolic orbit which I always thought meant it was not bound by the Sun’s gravity (and so would escape the Sun). But it seems comets can have hyperbolic orbits when in the inner solar system yet still have a closed orbit about the Sun.

If you are not sure you have seen comet ZTF look again the following night, using the chart above or your favourite astronomy app to guide your binoculars, and look for the fuzzy dot that has moved!

Can I see it by eye?

The predictions are that comet ZTF will be at its brightest in early February. It may be just bright enough to see with the naked eye when it is first visible from Australia. But you would need to be away from city lights and it helps to find the comet first with binoculars. By mid-February it will have dimmed a little, and as it climbs past the constellation Orion in later February it will be fading and becoming difficult to see even with binoculars.

When is the best viewing opportunity?

A great opportunity to spot comet ZTF is over the weekend of February 10-12. By 9pm each night the sky is dark and the Moon has not yet risen.

Look for planet Mars, the bright orange-reddish ‘star’ due north. Don’t mistake Mars for the fainter star Aldebaran, part of the triangular group of stars higher up. As the chart shows on Feb 10 comet ZTF is below and right of the planet, on the 11th it is just two Moon-widths to the right of Mars and on the 12th the comet is just above right of Mars.

The combination of fuzzy comet with the red planet will make a very photogenic combination!

Following this comet ZTF continues climbing higher in our southern skies, up past the constellation of Orion. As it does so it will be moving further from Earth and getting fainter.

What do we know about this comet?

Its name, C/2022 E3 (ZTF): ‘C/’ is the designation for a ‘non-periodic’ comet, but to astronomers ‘non-periodic’ means it has an orbital period (around the Sun) of over 200 years. Well, that is a long time for any one of us! ‘E3’ tells us about its discovery date – the 3rd comet found in the first half of March. There are 24 half-months in the year and 26 letters, so E corresponds to the first half of March. ‘(ZTF)’ was the entity that discovered it. In this case an automated telescope search program called the ‘Zwicky Transient Facility‘ – a program looking for anything in the sky that changes brightness or moves. There are many “comet ZTF’s”, but this is the only “C/2022 E3 (ZTF)”.

Comets are lumps of frozen ice, dust and rock that formed early in the life of the solar system. The ices include water ice, carbon-dioxide ice (dry ice), methane ice and other materials that are gasses here on Earth’s surface. The dust is composed of silicates and hydrocarbons. Somehow, possibly after passing close to one of the planets, it was thrown to the outer edges of the solar system, far beyond Neptune, to the Oort cloud. Noone has ever observed the Oort cloud directly, but the orbits of comets like this one imply it is there.

Comet ‘ZTF’ has arrived from the Oort cloud by coming ‘over the top’ of the Sun and over the north pole of Earth. It will swing down through the plane of the planets and head back out ‘under’ the Sun. Therefore, only since early February has it been visible from the southern hemisphere. Its orbital period is estimated to be over 50,000 years. On its last pass around the Sun it probably wasn’t seen by anyone. It’s only just visible to the eye on this pass, and on its last pass it was most likely further away and fainter still.

As comets reach the inner solar system, anywhere closer than about Saturn’s orbit, the Sun warms them up (just as the Sun warms your face on a winter’s day, or any day) and their gasses vaporise. This also releases the dust and rock. The dust trails behind the comet and is gently wafted away by the solar wind. The gasses can be ionized (or split) by sunlight and they stream radially away from the Sun. So we typically see a broad dust tail and a finer, gossamer ion tail. By eye (either naked or with your binoculars) you usually only see the more substantial dust tail. An ion tail may contain carbon in the form of two joined carbon atoms and if the sunlight splits these into individual carbon atoms the result is a greenish glow. Photographs will show the colour and the ion tail.

A final note…

There is one thing all comets are known for – their unpredictability!

Well, we know exactly where in the sky they will be. But their appearance is always unpredictable – they can fade suddenly, breakup completely and disappear, or even undergo an outburst (a large & sudden eruption of material from their surface) and brighten up significantly.

What exactly happens to comet C/2022 E3 (ZTF) we can only wait to see.

* A note on times: Australia’s several time zones and various daylight-saving preferences complicate the viewing times. The times quoted above are appropriate for NSW, ACT, Victoria & Tasmania. For Queensland replace ‘9pm AEDT’ with ‘8pm local time’. For South Australia replace ‘9pm AEDT’ with ‘9:30pm local time’. For the NT replace ‘9pm AEDT’ with ‘8:30pm local time’. And for Western Australia replace ‘9pm AEDT’ with ‘8pm local time’.