How to see Comet Leonard at its best

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Amateur astronomers are hopeful that a comet discovered in early 2021 could become bright enough to see with the unaided eye by mid December.

A stack of four photos of the comet taken on the morning of 4 December from Walmer, UK. Image credit: Paul Sutherland

Comet Leonard, officially labelled C/2021 A1 (Leonard), was discovered on 3 January when it still lay deep in the Solar System at a similar distance to Jupiter.

Its orbit shows it to be a long period comet, possibly on its first visit to the inner Solar System. Over recent weeks it has brightened to become visible with binoculars by the end of November, and fairly easy to record with a camera.

The comet, named after Gregory Leonard, who discovered it in from Mount Lemmon, Arizona, will be nearest to Earth on 12 December as it heads for perihelion its closest approach to the Sun on 3 January, 2022.

A chart showing the track of Comet Leonard during the first half of December. Positions are shown for 0h UT, in the date format month-day. Click to enlarge. Credit: Skymania using Cartes du Ciel

It will be visible against a dark sky during early December, and there are hopes that it could become quite bright with an obvious tail. Comet appearances are notoriously difficult to predict, but expectations range from a magnitude around 4 to a brighter magnitude 2.

Photographic images taken during November showed a clearly developing tail. In late November, the shape of the coma, or gas ball around the comet’s head, led to fears that the comet might be breaking up. However, subsequent observations of the comet showed these fears to be unfounded.

A processed and cropped stack of multiple images taken on 2 December from Kendal, UK, with a Canon 700D DSLR camera with 300mm lens, on an iOptron tracker mount. Image credit: Stuart Atkinson

At the end of November, the comet was easy to see with binoculars and its brightness was estimated to be around magnitude 6.

The best time to observe Comet Leonard is likely to be during the first two weeks of December. The comet will pass close to the bright star Arcturus in the constellation of Bootes, the Herdsman, as seen in the chart above.

This area of sky is visible low in the northwest after sunset, but in early December is much better placed a few hours later in the morning sky before dawn, when it will be higher above the horizon. After 12 December, it will probably be easier to see for a few nights in the evening twilight as it travels southwards along the western horizon.

More charts and information about seeing Comet Leonard are available on the website of the Society for Popular Astronomy’s Comet Section.

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