Saturday 30 July 2022

Comet C/2021 P4 (ATLAS) reaches perihelion.

Comet C/2021 P4 (ATLAS) reached its perihelion (the closest point on its orbit to the Sun) slightly after 9.00 am GMT on Saturday 30 July 2022, when it will be approximately 1.08 AU from the Sun (i.e. 1.08 times as far from the Sun as the planet Earth, or 161 360 000 km). At this time the comet is 1.95 AU from the Earth, in the constellation of Leo, having a magnitude of 12.55, making it visible with a telescope with an aperture of 250 mm or greater, making it fairly close to the Sun, and best observed slightly after dusk (extreme caution should be taken when observing objects close to the Sun, and an optical instrument should never be looked through when it is pointing close to the Sun).

The trajectory of Comet C/2021 P4 (ATLAS), and its current position. JPL Small Body Database.

C/2021 P4 (ATLAS) was discovered on 10 August 2021 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) search program. The name C/2021 P4 (ATLAS) implies that it is a comet (C/), that it was the fourth comet (4) discovered in the first half of August 2021 (period 2021 P) and that it was discovered by the ATLAS program.

Comet C/2021 P4 (ATLAS) is estimated to complete one orbit every 5574 years on an eccentric orbit tilted at 56.3° to the plane of the Solar System, that takes it from 1.08 AU from the Sun (108% of the average distance at which the Earth orbits the Sun) to 628 AU from the Sun (628 times as far from the Sun as the Earth, and roughly 21 times the distance at which the planet Neptune orbits the Sun). As a comet with an orbital period of more than 200 years it is considered to be a Long Period Comet; such comets are sometimes referred to as Non-periodic Comets, since there is no expectation of their being another observation being made by anyone who will remember the current comet naming-system, although this name does not distinguish them from Parabolic Comets, which are knocked from a position in the Oort Cloud by an encounter with some other object, and pass through the Inner Solar System once before disappearing into space, or Interstellar Comets, which originate outside the Solar System and only pass through it once.

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