2,283 days ago
Dominic Ford, Editor
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Comet 21P/Giacobini-Zinner is forecast to reach the brightest point in its 2018 apparition on 15 September. At that time, it will lie at a distance of 1.01 AU from the Sun, and at a distance of 0.32 AU from the Earth.
From Cambridge on 15 September it will be visible in the dawn sky, rising at 22:36 (EST) and reaching an altitude of 65° above the eastern horizon before fading from view as dawn breaks at around 05:14.
The events that comprise the 2018 apparition of 21P/Giacobini-Zinner are as follows:
| Date | Event |
| 14 Sep 2018 | Comet 21P/Giacobini-Zinner passes perihelion |
| 15 Sep 2018 | Comet 21P/Giacobini-Zinner reaches peak brightness |
| 15 Sep 2018 | Comet 21P/Giacobini-Zinner passes perigee |
The table below lists the times when 21P/Giacobini-Zinner will be visible from Cambridge day-by-day through its apparition:
| Date | Constellation | Comet visibility |
| 25 Aug 2018 | Cassiopeia | Visible from 20:41 until 04:48 Highest at 04:48, 62° above N horizon |
| 27 Aug 2018 | Camelopardalis | Visible from 20:37 until 04:51 Highest at 04:51, 63° above N horizon |
| 29 Aug 2018 | Camelopardalis | Visible from 20:33 until 04:53 Highest at 04:53, 64° above NE horizon |
| 31 Aug 2018 | Camelopardalis | Visible from 20:30 until 04:56 Highest at 04:56, 65° above NE horizon |
| 02 Sep 2018 | Camelopardalis | Visible from 22:44 until 04:58 Highest at 04:58, 66° above NE horizon |
| 04 Sep 2018 | Camelopardalis | Visible from 23:14 until 05:01 Highest at 05:01, 67° above NE horizon |
| 06 Sep 2018 | Auriga | Visible from 23:41 until 05:03 Highest at 05:03, 68° above NE horizon |
| 08 Sep 2018 | Auriga | Visible from 00:05 until 05:06 Highest at 05:06, 68° above NE horizon |
| 10 Sep 2018 | Auriga | Visible from 00:26 until 05:08 Highest at 05:08, 68° above E horizon |
| 12 Sep 2018 | Auriga | Visible from 00:45 until 05:10 Highest at 05:10, 67° above E horizon |
| 14 Sep 2018 | Auriga | Visible from 01:02 until 05:13 Highest at 05:13, 66° above E horizon |
| 16 Sep 2018 | Auriga | Visible from 01:18 until 05:15 Highest at 05:15, 64° above E horizon |
| 18 Sep 2018 | Gemini | Visible from 01:32 until 05:18 Highest at 05:18, 62° above SE horizon |
| 20 Sep 2018 | Gemini | Visible from 01:46 until 05:20 Highest at 05:20, 59° above SE horizon |
| 22 Sep 2018 | Gemini | Visible from 01:59 until 05:22 Highest at 05:22, 57° above SE horizon |
| 24 Sep 2018 | Gemini | Visible from 02:11 until 05:24 Highest at 05:24, 54° above SE horizon |
| 26 Sep 2018 | Monoceros | Visible from 02:22 until 05:27 Highest at 05:27, 51° above SE horizon |
| 28 Sep 2018 | Monoceros | Visible from 02:34 until 05:29 Highest at 05:29, 49° above SE horizon |
| 30 Sep 2018 | Monoceros | Visible from 02:45 until 05:31 Highest at 05:31, 46° above SE horizon |
| 02 Oct 2018 | Monoceros | Visible from 02:55 until 05:34 Highest at 05:34, 43° above SE horizon |
| 04 Oct 2018 | Monoceros | Visible from 03:05 until 05:36 Highest at 05:36, 41° above SE horizon |
A more detailed table of 21P/Giacobini-Zinner's position on each night is available here. A diagram of the orbit of 21P/Giacobini-Zinner is available here.
Finder chart
The chart below shows the path of 21P/Giacobini-Zinner 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.
No estimate for the brightness of comet 21P/Giacobini-Zinner is currently available.
The comet's position on 15 September 2018 will be:
| Object | Right Ascension | Declination | Constellation | Magnitude |
| Comet 21P/Giacobini-Zinner | 06h04m20s | 33°44'N | Auriga | 7.0 |
The coordinates are given in J2000.0.
The sky on 15 Sep 2018
| The sky on 15 September 2018 | ||||||||||||||||||||||||||||||||||
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42% 6 days old |
All times shown in EDT.
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Source
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 10 Dec 2024.
Image credit
© Andy Roberts 1997. Pictured comet is C/1995 O1 Hale-Bopp.