Comet C/2021 T4 (Lemmon) will make its closest approach to the Earth on 20 July, at a distance of of 0.54 AU.

From Cambridge on the day of perigee it will not be observable because it will lie so far south that it never rises above the horizon.

The events that comprise the 2023 apparition of C/2021 T4 (Lemmon) are as follows:

The table below lists the times when C/2021 T4 (Lemmon) will be visible from Cambridge day-by-day through its apparition:

A more detailed table of C/2021 T4 (Lemmon)'s position on each night is available here. A diagram of the orbit of C/2021 T4 (Lemmon) is available here.

Finder chart

The chart below shows the path of C/2021 T4 (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.

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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 For most comets, we do not publish any magnitude estimates at all.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 20 July 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 perigee will be:

The coordinates are given in J2000.0.

The sky on 20 Jul 2023

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 18 Nov 2024.

Image credit

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

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