Comet C/2021 A1 Leonard could put on a beautiful display this December

By Pete Lawrence

Published: Friday, 26 November 2021 at 12:00 am

At the start of 2021, newly discovered comet C/2021 A1 Leonard was announced. Excitingly this has the possibility of becoming bright during December 2021 and exceeding the threshold of naked-eye visibility in the run-up to Christmas.

Comet Leonard was discovered by astronomer Greg Leonard at the start of 2021, and images taken recently already show a decent coma and tail.

This has many speculating we may see enthusiasm and interest in Comet Leonard reach a peak in December, similar to what we saw in 2020 with Comet NEOWISE, which made headlines around the globe.

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Comet C/2021 A1 (Leonard) photographed at 11:38 UTC on 5 October 2021 by José J. Chambo, from Mayhill, New Mexico, USA. Equipment: FLI PL6303E camera, Planewave 17″ CDK f/4.5 telescope. Exposure 8 min. (L=1×300 bin1 + RGB=1×60 bin2) www.cometografia.es

Indeed, as comet-chaser José J. Chambó notes in an image captured by him (below) on 4 November 2021 from Mayhill, New Mexico, USA, Comet Leonard is already showing an increase in brightness, especially when compared to a previous image captured by José on 5 October (above).

This could mean we’ll get a good display in December.

“Since my previous image its look has changed dramatically: in just two weeks its brightness has increased from magnitude 11.5 to 10,” says José of his 4 November shot.

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Comet C/2021 A1 (Leonard), photographed by José J. Chambo at 11:49 UTC on 4 November 2021 from Mayhill, New Mexico, USA. Equipment: FLI PL6303E camera, Planewave 17″ CDK f/4.5 telescope. Exposure 12 min. (L=3×180 bin1 + RGB=1×60 bin2). www.cometografia.es

“Its coma has increased in angular size from 4′ to 9′ having developed an strong outer halo of intense green colour, and its tail has grown from 5′ to 16′ in length.

“Everything continues signalling that the comet is very active and it keeps the expectation of being observable at naked eye in December.”

Keep up to date with José’s comet-chasing via his website Cometografía.

Will Comet Leonard be visible?

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The evening appearance of Comet A1 Leonard after sunset. It appears near Venus on 18 December, when it physically passes the planet at 0.029 AU. Credit: Pete Lawrence

Current estimates have Comet Leonard positioned near mag. +4.3 Beta (β) Comae Berenices on 1 December, shining at mag. +9.3.

It’s then expected to brighten to about seventh magnitude mid-month, making it an easy object to observe through binoculars.

An effect known as forward-scattering enhancement may boost its brightness so it becomes visible to the naked eye.

Forward-scattering enhancement may help A1 Leonard become visible to the naked eye between 10–16 December, peaking at mag. +4.0 around 13 December.

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Comet A1 Leonard’s path during December’s first half. Credit: Pete Lawrence

How to see Comet Leonard from the UK

The best prospects of seeing Comet Leonard from the UK will be during the mornings of 1–13 December.

Its morning track is shown at the top of of this section, while just above we’ve shown how the comet moves relative to Venus in the evening sky.

Unless the comet brightens more than expected, the evening appearance will probably go unnoticed from the UK due to low altitude.