Grab a pair of binoculars and find a dark spot and you may catch a glimpse of the "Christmas comet" over the next two weeks.
C/2021 A1 (Leonard), aka Comet Leonard, is an icy interloper from the far reaches of our Solar System that hasn't been seen for thousands of years — and will never be seen again.
Despite earlier fears Comet Leonard might break apart, it passed by Earth last week and suddenly became brighter so it could be seen with the naked eye in the northern hemisphere.
Although the comet has dimmed again, it is bright enough that it you may be able to see it with binoculars, especially if you are in a dark sky location.
Comet Leonard has just moved into view in the southern hemisphere, and if it continues to hold together, Australian sky watchers may catch it as it streaks towards the Sun.
Hopefully it will put on a good show, says Dylan O'Donnell, an astronomer and astrophotographer based in Byron Bay.
"It's probably the most exciting thing in the sky this year, apart from the lunar eclipse," he says.
Here's how to spot it and take the best photos.
Where to spot Comet Leonard
The comet makes its closest approach to Venus later today (December 18) just after 1pm (AEDT).
Passing just 4 million kilometres away, it's the nearest a comet will sweep past Venus in recorded history, says astronomer Jonti Horner of the University of Southern Queensland.
"That means from the point of view of Venus, it will be really, really spectacular," he says.
There is even a chance that as it passes by, it will kick up some dust and create a meteor shower over our neighbour.
Back on Earth, it will appear as a fuzzy blob spot sitting just to the left of Venus on the western horizon just after sunset (local time).
But getting your timing right is critical as the comet sets below the horizon just as twilight ends.
"Photographers are competing against the retreating Sun and setting comet at the same moment," Mr O'Donnell says.
To get the best view you'll need to find somewhere with a clear view of the horizon and get away from lights.
The full moon will also be in the sky on Saturday night, but Mr O'Donnell doesn't think this will interfere much.
"The Moon will be rising in the east just as the comet is setting on the west, so hopefully it shouldn't wash out the comet too much," he says.
Each night the comet will be higher in the sky as it moves further from Earth.
"As it appears to get higher over Venus, it will be easier to see against the darkness of the sky," Mr O'Donnell says.
By Christmas night it should be lined up to the left of Jupiter.
What will Comet Leonard look like?
Comets have two tails — a gas tail and a dust tail — that always stretch away from the Sun.
"Which one dominates depends upon the composition of the comet," Professor Horner says.
The dust tail tends to be a bit curved as the dust is pushed away from the Sun, while the gas tail tends to be straight, but can develop kinks as it goes through different parts of the solar wind.
"The dust tail is usually fairly neutral in colour, whitish or yellowish, and the gas tail tends to be blue because the gas has been ionised [had electrons stripped off it]," Professor Horner says.
But you'll need a camera to see the comet's colours, because your eye is not as sensitive to colour at night.
Photos taken from the northern hemisphere, where the comet was visible last week as it passed Earth, show a blue gas halo with a straight tail.
The latest reports indicate the comet is currently bright enough to see with binoculars over Australia as a fuzzy dot in the twilight sky.
We may see more of the tail over the next day or so while it is still close to the Sun from our viewing perspective due to a phenomenon known as forward scattering.
That's when sunlight backlights the comet's tail, making it appear brighter.
The comet may also appear brighter again if it has another outburst of gas from its head as travels in towards the Sun and heats up.
But if the comet doesn't have any outbursts it will get gradually fainter each night as it moves further away from Earth.
How to take the best photo of Comet Leonard
Taking images of comets is about as dynamic as it gets for photographers, Mr O'Donnell says.
"Their size, brightness and position all change from night to night, which makes it hard to predict how to photograph them," he says.
But any camera and lens should be fine as long as you take an exposure of a few seconds or more.
"I'd recommend starting with an ISO of around 800, your aperture wide open (lower f number) and start with a 2-second exposure," he says.
"Adjust your exposure time to be longer, or your ISO to be higher, if your photo is too dark."
If you get lucky with the weather, you may have an hour or more to play with the settings and get a photo that reveals the comet against a starry sky, he adds.
"In an average photo you'll be able to make out what looks like a blurry star. This might even be possible with a smartphone.
"With a good shot you'll see the tail as well, and possibly the characteristic green of the coma [comet's head]."
If you have a telephoto lens around 200mm you should be able to fit the comet's head and tail into one image, but wider landscape lenses are also fine, and will let you see the comet against a wide star field, he says.
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