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

Comet C/2023 H2 (Lemmon) passes perihelion

Dominic Ford, Editor
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Comet C/2023 H2 (Lemmon) will make its closest approach to the Sun on 29 October, at a distance of 0.89 AU.

From Ashburn on the day of perihelion it will be visible in the dawn sky, rising at 00:46 (EST) and reaching an altitude of 30° above the north-eastern horizon before fading from view as dawn breaks at around 06:27.

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The events that comprise the 2023 apparition of C/2023 H2 (Lemmon) are as follows:

Date Event
29 Oct 2023Comet C/2023 H2 (Lemmon) passes perihelion
10 Nov 2023Comet C/2023 H2 (Lemmon) passes perigee
10 Nov 2023Comet C/2023 H2 (Lemmon) reaches peak brightness

The table below lists the times when C/2023 H2 (Lemmon) will be visible from Ashburn day-by-day through its apparition:

Date Constellation Comet visibility
08 Oct 2023Ursa MajorVisible from 05:38 until 06:06
Highest at 06:06, 26° above NE horizon
10 Oct 2023Canes VenaticiVisible from 05:33 until 06:08
Highest at 06:08, 27° above NE horizon
12 Oct 2023Canes VenaticiVisible from 05:27 until 06:10
Highest at 06:10, 28° above NE horizon
14 Oct 2023Canes VenaticiVisible from 05:22 until 06:12
Highest at 06:12, 29° above NE horizon
16 Oct 2023Canes VenaticiVisible from 05:18 until 06:14
Highest at 06:14, 30° above NE horizon
18 Oct 2023Canes VenaticiVisible from 05:14 until 06:16
Highest at 06:16, 31° above NE horizon
20 Oct 2023Canes VenaticiVisible from 05:11 until 06:18
Highest at 06:18, 31° above NE horizon
22 Oct 2023Canes VenaticiVisible from 05:10 until 06:20
Highest at 06:20, 32° above NE horizon
24 Oct 2023Canes VenaticiVisible from 05:11 until 06:22
Highest at 06:22, 32° above NE horizon
26 Oct 2023Canes VenaticiVisible from 05:14 until 06:24
Highest at 06:24, 32° above NE horizon
28 Oct 2023Canes VenaticiVisible from 05:22 until 06:26
Highest at 06:26, 31° above NE horizon
30 Oct 2023Ursa MajorVisible from 19:15 until 19:17
05:35 until 06:28
Highest at 06:28, 29° above NE horizon
01 Nov 2023BootesVisible from 19:13 until 19:38
05:58 until 06:30
Highest at 06:30, 26° above NE horizon
03 Nov 2023BootesVisible from 19:11 until 20:06
Highest at 19:11, 30° above NW horizon
05 Nov 2023HerculesVisible from 18:09 until 19:38
Highest at 18:09, 36° above NW horizon
07 Nov 2023HerculesVisible from 18:08 until 20:11
Highest at 18:08, 43° above W horizon
09 Nov 2023HerculesVisible from 18:06 until 20:35
Highest at 18:06, 50° above W horizon
11 Nov 2023AquilaVisible from 18:04 until 20:39
Highest at 18:04, 50° above SW horizon
13 Nov 2023AquilaVisible from 18:03 until 20:25
Highest at 18:03, 42° above SW horizon
15 Nov 2023CapricornusVisible from 18:01 until 20:02
Highest at 18:01, 35° above S horizon
17 Nov 2023CapricornusVisible from 18:00 until 19:31
Highest at 18:00, 28° above S horizon

A more detailed table of C/2023 H2 (Lemmon)'s position on each night is available here. A diagram of the orbit of C/2023 H2 (Lemmon) is available here.

Finder chart

The chart below shows the path of C/2023 H2 (Lemmon) 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 on 29 October 2023. 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/2023 H2 (Lemmon) 13h34m10s 50°05'N 8.5

The coordinates are given in J2000.0.

The sky on 29 Oct 2023

The sky on 29 October 2023
Twilight ends
Twilight begins

15-day old moon
Waning Gibbous


15 days old

Rise Culm. Set
Mercury 08:04 13:15 18:26
Venus 03:42 10:00 16:18
Moon 18:05 01:08 08:25
Mars 08:03 13:15 18:27
Jupiter 18:27 01:16 08:04
Saturn 15:29 20:49 02:09
All times shown in EDT.


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 09 Dec 2023.

Image credit

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





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