Comet 21P/Giacobini-Zinner will make its closest approach to the Sun on 31 December, at a distance of 1.01 AU.

From South El Monte on the day of perihelion it will be visible in the evening sky, becoming accessible around 18:00 (PDT), 26° above your north-eastern horizon, as dusk fades to darkness. It will then reach its highest point in the sky at 23:14, 89° above your northern horizon. It will continue to be observable until around 04:54, when it sinks below 21° above your north-western horizon.

The events that comprise the 1969–1970 apparition of 21P/Giacobini-Zinner are as follows:

The table below lists the times when 21P/Giacobini-Zinner will be visible from South El Monte day-by-day through its apparition:

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 For most comets, we do not publish any magnitude estimates at all.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 at perihelion will be:

The coordinates are given in J2000.0.

The sky on 10 Oct 2025

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 29 Sep 2025.

Image credit

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

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