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

C/2020 S3 (Erasmus) at perigee

Dominic Ford, Editor
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Comet C/2020 S3 (Erasmus) will make its closest approach to the Earth, at a distance of 1.03 AU.

The comet's perigee – closest approach to Earth – should not be confused with its perihelion, when it passes closest to the Sun. Comets become much brighter when they pass close to the Sun. At perihelion their surfaces are heated and produce clouds of dust which give rise to their tails and extended coma around the nucleus. As a result, most comets are brightest around the time of their perihelion, not their perigee.

From Ashburn the 2020–2021 apparition of C/2020 S3 (Erasmus) will progress as follows:

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18 Nov 2020 – C/2020 S3 (Erasmus) at perigee
12 Dec 2020 – C/2020 S3 (Erasmus) at perihelion
28 Oct 2020SextansVisible from 05:13 until 06:27
Highest at 06:27, 33° above SE horizon
30 Oct 2020SextansVisible from 05:22 until 06:28
Highest at 06:28, 32° above SE horizon
01 Nov 2020SextansVisible from 04:31 until 05:30
Highest at 05:30, 31° above SE horizon
03 Nov 2020SextansVisible from 04:42 until 05:32
Highest at 05:32, 29° above SE horizon
05 Nov 2020CraterVisible from 04:54 until 05:34
Highest at 05:34, 28° above SE horizon
07 Nov 2020CraterVisible from 05:06 until 05:36
Highest at 05:36, 26° above SE horizon
09 Nov 2020CraterVisible from 05:20 until 05:38
Highest at 05:38, 25° above SE horizon
11 Nov 2020CraterVisible from 05:35 until 05:40
Highest at 05:40, 23° above SE horizon
13 Nov 2020CorvusNot observable
15 Nov 2020CorvusNot observable
17 Nov 2020CorvusNot observable
19 Nov 2020CorvusNot observable
21 Nov 2020VirgoNot observable
23 Nov 2020VirgoNot observable
25 Nov 2020VirgoNot observable
27 Nov 2020HydraNot observable
29 Nov 2020LibraNot observable
01 Dec 2020LibraNot observable
03 Dec 2020LibraNot observable
05 Dec 2020LibraNot observable
07 Dec 2020LibraNot observable

A more detailed table of C/2020 S3 (Erasmus)'s position on each night is available here. A diagram of the orbit of C/2020 S3 (Erasmus) is available here.

Finder chart

The chart below shows the path of C/2020 S3 (Erasmus) 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 8 at perigee. 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 at perihelion will be:

Object Right Ascension Declination Constellation Magnitude
Comet C/2020 S3 (Erasmus) 12h38m10s 19°15'S Corvus 7.7

The coordinates are given in J2000.0.

The sky on 18 November 2020
Twilight ends
Twilight begins

3-day old moon
Waxing Crescent


3 days old

Rise Culm. Set
Mercury 05:28 10:48 16:09
Venus 04:21 09:57 15:32
Moon 10:44 15:27 20:11
Mars 14:51 21:12 03:32
Jupiter 11:11 15:58 20:46
Saturn 11:22 16:13 21:03
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 25 Jan 2022.

Image credit

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






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