Update, Dec 21: I managed to see comet Leonard from dark, rural skies west of Sydney on the night of Dec 20 at 9:15pm. I had to use binoculars but my observing companion saw it naked eye. It was between magnitude 4 & 5, above & left of Venus, looked like a fuzzy star (i.e. clearly extended) but with no tail visible. So, I will update my notes below to suggest looking after 9pm over the next few days before Christmas. You can use the chart above to estimate where it ill be each night. Or use your favourite astronomy app…

Update, Dec 23: I managed to see comet Leonard again on the evening of Dec 21 with a Meade 10-inch SCT. It was just vdetectable to my naked eye once the telescope was pointing at it. I took the snapshot below. Otherwise its been cloudy.

Comet C/2021 A1 (Leonard) on 2021Dec21 at 21:35 AEDT (10:35UT) from near Lithgow, NSW. Meade 10-inch SCT, eyepiece projection, iPhone8, NexYZ phone holder,  ISO800, 120sec. Processed to adjust contrast only. Photo copyright MAAS.

This weekend may be your best chance to see a comet this year

Comet 2021 A1 (Leonard) has been visible from the northern hemisphere (with binoculars) for the last few weeks. There are some lovely images at Space Weather. Now it’s our turn in the southern hemisphere as the comet moves below the plane of Earth’s orbit around the Sun, and into the western evening sky. Our best opportuity to see this comet is this weekend, December 17 to 19, 2021.

To see this comet look to the west at 8:30pm. First, you will easily spot by eye the very bright planet Venus, shining like a beacon and about a handspan (if you hold you hand out at arm’s length) above the horizon. Now, with a pair of binoculars, look at Venus. You may be able to see it has a crescent shape, like a crescent Moon. But to see the comet…

• On Friday 17th December move your binoculars diagonally down and left till Venus just disappears from view. With luck you may now see the comet. It will appear as a fuzzy spot, like an out of focus star, and may just have a hint of a tail stretching up and right, back towards Venus.
• On Saturday 18th December find Venus again, but this time move the binoculars directly to the left, again till Venus just disappears. Hopefully, the comet is brighter tonight. Any tail, if visible, will still be pointing up & right. Comet tails always point away from the Sun.
• On Sunday 19th December, look above and left of Venus with your binoculars, moving them again till Venus just disappears.

Now, comets seem to have minds of their own and they do exactly as they please. So we have no idea whether comet Leonard will brighten up, or fade quickly. It may become easily visible to the naked eye, Great! Or it may fade away and not even be visible in your binoculars. Oh Well, maybe next year! Yes, its a bit like coping with covid, we just have to be ready for it, but be prepared to change plans at short notice!

If comet Leonard brightens it may be visible into next week, and reallly become a Christmas Comet. However, while the comet is moving higher into the sky (and so should be easier to see each night in the darkening sky) it is also moving away from Earth, so it’s therefore getting fainter. How these two effects balance out will determine how bright, and how visible the comet will be.

This comet was discovered in January this year (hence its designation of “2021 A1”) by Greg Leonard at the Mt Lemmon observatory in the USA. It has spent over 35,000 years falling towards the Sun from far beyond Pluto. It passed the Earth (at 35 million kilometres) on December 12 and will pass (relatively) close to Venus this weekend – not just close in the sky, but close in space too.

Good Luck!