Comet Leonard: Meet the “Christmas Comet”!

~3 min

Comet Leonard, discovered at the beginning of 2021, will get closest to the Earth this December – hence the nickname “Christmas comet”. Read on to find out when and how to see the brightest comet of the year in the sky.

What is Comet Leonard?

On January 3, 2021, American astronomer Gregory J. Leonard discovered a new comet at the Mount Lemmon Observatory in Arizona, USA. It was named C/2021 A1 (Leonard) – the letter “C” means “non-periodic comet”, and “2021 A1” indicates that it was the first comet discovered in the first half of January 2021.

A specific feature of Comet Leonard is its incredible speed – about 70 km/s (43 mi/s)! It’s moving six km/s (three mi/s) faster than last year’s comet NEOWISE. Due to such speed, the comet’s position in the sky will be changing every day when we observe it from the Earth.

Comet Leonard has a hyperbolic trajectory, which means that it will cross the Solar System only once and then move far away from us and will never come back. So, you’ll only have one chance to see it.

When will Comet Leonard be best visible?

The comet will get closest to the Earth and will be best visible on December 12, 2021. It will pass by our planet at a distance of 34 million km (21 million mi), shining with a magnitude of about 4. As the comet will be positioned between the Sun and the Earth at this moment, its magnitude can even reach 1 due to the effect of forward scattering. This means that you’ll be able to see Comet Leonard through binoculars or even with the naked eye!

What will Comet Leonard look like?

When the comet reaches maximum brightness, it will have a dust tail and a gas tail. The dust tail will be shaped like a spike: this will happen because on December 8, the Earth will cross the orbital plane of the comet, and observers will view the dust tail edge-on. The viewing angle will cause the tail to narrow and brighten a bit.

Comet Leonard has already grown a long gas (ion) tail – it is now twice the angular size of a Full Moon! The direction of the dust and gas tails will be the same for most of the time the comet will be observable. Only in the period from December 10 to December 13, the two tails will form a visible angle that will not exceed 30°.

The comet might also have an antitail that will seem to point in the direction opposite the other tails – towards the Sun. In fact, an antitail is an optical illusion that is created when we view larger dust particles deposited along a comet's orbit edge-on.

When can I start observing Comet Leonard?

If you live in the northern mid-latitudes, you can start observing the comet right now! Currently, Comet Leonard has a visual magnitude of about 5; it can be seen through a telescope or binoculars during the predawn hours. Look for the comet in the constellation Bootes, below Ursa Major. A good reference point will be Arcturus — the brightest star in Bootes and one of the brightest stars in the sky. The comet will pass close to Arcturus on December 6-7.

When Comet Leonard reaches maximum brightness on December 12, it will be positioned in the constellation Ophiuchus. By this date — if we’re lucky — it may become visible to the naked eye!

In the second half of December, the comet will move into the southern celestial hemisphere. On Christmas Day (December 25), Comet Leonard will be visible from the Southern Hemisphere in the constellation Microscopium. To quickly find the comet’s location in the sky, use our stargazing apps: Sky Tonight or Star Walk. Launch any of these apps, tap the magnifier icon, type “Leonard” in the search field, and the app will show you the comet’s exact location.

Is Comet Leonard disintegrating?

Some observers express concerns about Comet Leonard’s “well-being”. There are three main signs that the comet could be falling apart:

  • It’s not brightening as rapidly as it used to;
  • Its coma has become flattened from the side facing the Sun;
  • It seems to be affected by non-gravitational forces caused by gases leaving the comet’s surface.

However, it is still too early to say if the comet is in any danger. All we can do is wait and hope for the best.

Comet Leonard may not become “the new Neowise”, but it can still provide a spectacular astronomical show by the end of 2021. Let’s keep our fingers crossed for that! We wish you clear skies and happy observations!