© Andy Roberts 1997. Pictured comet is C/1995 O1 Hale-Bopp.

Comet C/2021 A1 (Leonard) passes perihelion

Dominic Ford, Editor
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Comet C/2021 A1 (Leonard) will make its closest approach to the Sun on 3 January, at a distance of 0.62 AU.

From Cambridge on the day of perihelion it will not be readily observable since it will lie so far south that it will never rise more than 11° above the horizon.

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The events that comprise the 2021–2022 apparition of C/2021 A1 (Leonard) are as follows:

Date Event
12 Dec 2021Comet C/2021 A1 (Leonard) passes perigee
03 Jan 2022Comet C/2021 A1 (Leonard) passes perihelion

The table below lists the times when C/2021 A1 (Leonard) will be visible from Cambridge day-by-day through its apparition:

Date Constellation Comet visibility
13 Dec 2021Serpens CaudaNot observable
15 Dec 2021SagittariusNot observable
17 Dec 2021SagittariusNot observable
19 Dec 2021SagittariusNot observable
21 Dec 2021MicroscopiumNot observable
23 Dec 2021MicroscopiumNot observable
25 Dec 2021MicroscopiumNot observable
27 Dec 2021MicroscopiumNot observable
29 Dec 2021Piscis AustrinusNot observable
31 Dec 2021Piscis AustrinusNot observable
02 Jan 2022Piscis AustrinusNot observable
04 Jan 2022Piscis AustrinusNot observable
06 Jan 2022Piscis AustrinusNot observable
08 Jan 2022Piscis AustrinusNot observable
10 Jan 2022Piscis AustrinusNot observable
12 Jan 2022Piscis AustrinusNot observable
14 Jan 2022Piscis AustrinusNot observable
16 Jan 2022Piscis AustrinusNot observable
18 Jan 2022Piscis AustrinusNot observable
20 Jan 2022Piscis AustrinusNot observable
22 Jan 2022Piscis AustrinusNot observable

A more detailed table of C/2021 A1 (Leonard)'s position on each night is available here. A diagram of the orbit of C/2021 A1 (Leonard) is available here.

Finder chart

The chart below shows the path of C/2021 A1 (Leonard) over the course of its apparition, as calculated from the orbital elements published by the Minor Planet Center (MPC). It is available for download, either on dark background, in PNG, PDF or SVG formats, or on a light background, in PNG, PDF or SVG formats. It was produced using StarCharter.

Comet brightnesses

Comets are intrinsically highly unpredictable objects, since their brightness depends on the scattering of sunlight from dust particles in the comet's coma and tail. This dust is continually streaming away from the comet's nucleus, and its density at any particular time is governed by the rate of sublimation of the ice in the comet's nucleus, as it is heated by the Sun's rays. It also depends on the amount of dust that is mixed in with that ice. This is very difficult to predict in advance, and can be highly variable even between successive apparitions of the same comet.

In consequence, while the future positions of comets are usually known with a high degree of confidence, their future brightnesses are not. For most comets, we do not publish any magnitude estimates at all. For the few comets where we do make estimates, we generally prefer the BAA's magnitude parameters to those published by the Minor Planet Center, since they are typically updated more often.

Based on the magnitude parameters published for this comet by the BAA Comet Section, we estimate that it may be around mag 6 on 3 January 2022. This estimate is based on observations that the BAA has received from amateur astronomers, assuming that its current level of activity will remain constant.

The comet's position at perihelion will be:

Object Right Ascension Declination Constellation Magnitude
Comet C/2021 A1 (Leonard) 21h38m10s 35°48'S 5.5

The coordinates are given in J2000.0.

The sky on 03 Jan 2022

The sky on 03 January 2022
Twilight ends
Twilight begins

1-day old moon
Waxing Crescent


1 day old

Rise Culm. Set
Mercury 08:27 13:07 17:48
Venus 07:28 12:22 17:15
Moon 08:20 12:48 17:21
Mars 05:11 09:45 14:18
Jupiter 09:45 15:03 20:21
Saturn 08:54 13:49 18:43
All times shown in EST.


This event was automatically generated on the basis of orbital elements published by the Minor Planet Center (MPC) , and is updated whenever new elements become available. It was last updated on 27 Feb 2023.

Image credit

© Andy Roberts 1997. Pictured comet is C/1995 O1 Hale-Bopp.






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