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

Comet C/2021 S3 (PANSTARRS) reaches peak brightness

Dominic Ford, Editor
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Comet C/2021 S3 (PANSTARRS) is forecast to reach the brightest point in its 2024 apparition on 1 March. At that time, it will lie at a distance of 1.34 AU from the Sun, and at a distance of 1.32 AU from the Earth.

From Ashburn on 1 March it will be visible in the dawn sky, rising at 01:56 (EST) and reaching an altitude of 37° above the south-eastern horizon before fading from view as dawn breaks at around 05:36.

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The events that comprise the 2024 apparition of C/2021 S3 (PANSTARRS) are as follows:

Date Event
14 Feb 2024Comet C/2021 S3 (PANSTARRS) passes perihelion
01 Mar 2024Comet C/2021 S3 (PANSTARRS) reaches peak brightness
14 Mar 2024Comet C/2021 S3 (PANSTARRS) passes perigee

The table below lists the times when C/2021 S3 (PANSTARRS) will be visible from Ashburn day-by-day through its apparition:

Date Constellation Comet visibility
09 Feb 2024OphiuchusVisible from 05:46 until 06:02
Highest at 06:02, 24° above SE horizon
11 Feb 2024OphiuchusVisible from 05:34 until 06:00
Highest at 06:00, 25° above SE horizon
13 Feb 2024OphiuchusVisible from 05:23 until 05:58
Highest at 05:58, 26° above SE horizon
15 Feb 2024OphiuchusVisible from 05:12 until 05:56
Highest at 05:56, 27° above SE horizon
17 Feb 2024Serpens CaudaVisible from 05:01 until 05:53
Highest at 05:53, 28° above SE horizon
19 Feb 2024Serpens CaudaVisible from 04:51 until 05:51
Highest at 05:51, 30° above SE horizon
21 Feb 2024Serpens CaudaVisible from 04:41 until 05:48
Highest at 05:48, 31° above SE horizon
23 Feb 2024Serpens CaudaVisible from 04:31 until 05:46
Highest at 05:46, 32° above SE horizon
25 Feb 2024OphiuchusVisible from 04:21 until 05:43
Highest at 05:43, 34° above SE horizon
27 Feb 2024Serpens CaudaVisible from 04:12 until 05:41
Highest at 05:41, 35° above SE horizon
29 Feb 2024Serpens CaudaVisible from 04:02 until 05:38
Highest at 05:38, 37° above SE horizon
02 Mar 2024Serpens CaudaVisible from 03:53 until 05:35
Highest at 05:35, 38° above SE horizon
04 Mar 2024Serpens CaudaVisible from 03:44 until 05:32
Highest at 05:32, 39° above SE horizon
06 Mar 2024Serpens CaudaVisible from 03:34 until 05:29
Highest at 05:29, 41° above SE horizon
08 Mar 2024Serpens CaudaVisible from 03:25 until 05:26
Highest at 05:26, 42° above SE horizon
10 Mar 2024Serpens CaudaVisible from 04:16 until 06:23
Highest at 06:23, 44° above SE horizon
12 Mar 2024Serpens CaudaVisible from 04:08 until 06:20
Highest at 06:20, 45° above SE horizon
14 Mar 2024AquilaVisible from 03:59 until 06:17
Highest at 06:17, 46° above SE horizon
16 Mar 2024AquilaVisible from 03:50 until 06:14
Highest at 06:14, 48° above SE horizon
18 Mar 2024AquilaVisible from 03:41 until 06:10
Highest at 06:10, 49° above SE horizon
20 Mar 2024AquilaVisible from 03:33 until 06:07
Highest at 06:07, 50° above SE horizon

A more detailed table of C/2021 S3 (PANSTARRS)'s position on each night is available here. A diagram of the orbit of C/2021 S3 (PANSTARRS) is available here.

Finder chart

The chart below shows the path of C/2021 S3 (PANSTARRS) 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 9 on 1 March 2024. This estimate is based on observations that the BAA has received from amateur astronomers, assuming that its current level of activity will remain constant.

This comet is not expected to be visible to the naked eye, but might be visible through bird-watching binoculars.

The comet's position on 1 March 2024 will be:

Object Right Ascension Declination Constellation Magnitude
Comet C/2021 S3 (PANSTARRS) 18h11m50s 5°11'S 8.7

The coordinates are given in J2000.0.

The sky on 1 Mar 2024

The sky on 1 March 2024
Twilight ends
Twilight begins

21-day old moon
Waning Gibbous


21 days old

Rise Culm. Set
Mercury 06:54 12:30 18:07
Venus 05:41 10:49 15:56
Moon 23:07 04:17 09:19
Mars 05:31 10:33 15:36
Jupiter 09:14 16:05 22:55
Saturn 06:45 12:17 17:49
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 04 Nov 2023.

Image credit

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





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