Astronomy Essentials

Comet Leonard: Now’s the time to start watching

Green comet with a nice tail.
View at EarthSky Community Photos. | Patrick Prokop in Savannah, Georgia captured 24 2-minute exposures of Comet Leonard on November 27, 2021 around 5 a.m. to create this beautiful composite image. Thank you, Patrick! Submit your comet image to EarthSky.

2021’s best comet

A much-anticipated comet – C/2021 A1 (Leonard) – is likely to be 2021’s best comet, and its brightest comet by year’s end. Astronomer Greg Leonard discovered the comet as 2021 began. Discovery images showed a tail for the comet, suggesting we might see a nice tail as Comet Leonard draws closer to the Earth and sun. And telescopic observers and astrophotographers do now see a tail, as photos on this page show. The comet is currently heading sunward, toward its perihelion or closest point to the sun on January 3, 2022. Comets are typically brightest around perihelion. Comet Leonard has been in the morning sky, but, in December, itll become visible in the evening sky. All in all, it’s time to look for a comet!

Over the coming month, as Comet Leonard heads sunward, it’ll sweep closest to Earth on December 13. It won’t be particularly close at its closest, passing more than 21 million miles (34 million km) away. But five days later – on December 18 – the comet will have an exceptionally close pass of Venus of just 2.6 million miles (4.2 million km). Then it’ll round the sun on January 3, 2022, at a distance of about 56 million miles (0.6 AU, or 90 million km).

According to TheSkyLive on September 28:

The current estimated magnitude [brightness] of Comet Leonard (C/2021 A1) is 10.64 (JPL) while the latest observed magnitude is 8.6 (COBS).

So, again, Comet Leonard is too faint to see with the eye. But it’s a good binocular comet now and might be possible to be glimpsed with the eye alone in dark skies as 2021 draws to a close.

Or maybe not. Comets are unpredictable. But C/2021 A1 (Leonard) is very much a comet worth watching.

Star chart with Big Dipper, Arcturus, and location of comet in tick marks.
Location of Comet C/2021 A1 (Leonard) on December 1, 2021. This chart is as seen from U.S., facing east about 90 minutes before sunrise. The Big Dipper asterism in the constellation Ursa Major the Great Bear will be in the northeast. It’ll provide a good reference for observers to locate the comet. Binoculars should provide a nice view. A dark sky is essential. Illustration by Eddie Irizarry using Stellarium. More charts below.

How bright will Comet Leonard get?

Will the comet get bright enough to see with the eye in December? It’s possible that Comet Leonard might reach 4th magnitude before its early January perihelion. Comets are diffuse bodies, not pinpoints, so a 4th-magnitude comet won’t appear as bright to your eye as a 4th-magnitude star. The star would be easily visible in a dark sky. The comet? At 4th magnitude, it would be a good binocular comet. It would be fun to see!

Nature provides us with sky events seen once in a lifetime. Comet Leonard might be one of these, if it gets bright enough.

If you do see it, at this sweep near the sun, it’ll truly be a once-in-a-lifetime event. This comet takes tens of thousands of years to complete an orbit around the sun. As Bob King pointed out at Skyandtelescope.com in October 2021:

Orbital calculations revealed that the object had spent the last 35,000 years wending its way sunward after reaching aphelion at the chilling distance of around 3,500 AU (3,500 times the distance between our Earth and sun].

In other words, after this current close sweep past our sun, we will not see Comet Leonard again.

Will you see this comet?

This comet is initially in Northern Hemisphere skies. But it will become visible from the Southern Hemisphere in December 2021 and January 2022.

An amazing feature of this celestial visitor is that it’s an ultrafast comet. It’s traveling at 158,084 miles per hour (254,412 km/h or 70.67 km/second) relative to Earth.

Despite its incredible speed through the vast space of our solar system, don’t expect to see this comet swoosh across the sky. Like planets, comets do move in front of the star background, but only very slowly due to the large distances involved. Observers using telescopes will have to take a close look at the comet’s position relative to background stars. Then compare the view five or 10 minutes later to detect its motion, because its great distance will cause it to appear as a very slow moving object.

Here are a few charts …

Comet Leonard before sunrise

Chart with constellations and tick marks for location of comet Leonard.
Location of Comet Leonard on November 30, 2021, about one hour before sunrise. By this date, the celestial visitor should be an easy target using binoculars. Comet Leonard will be located between the moon (on right, illuminated just around 19%) and the Big Dipper (upper left), facing east before sunrise. Illustration by Eddie Irizarry/ Stellarium.
Star chart with Big Dipper, Arcturus, and location of comet in tick marks.
Location of Comet C/2021 A1 (Leonard) on December 1, 2021. This chart is as seen from U.S., facing east about 90 minutes before sunrise. The Big Dipper asterism in the constellation Ursa Major the Great Bear will provide a good reference for observers to locate the comet. Binoculars should provide a nice view. Illustration by Eddie Irizarry using Stellarium.
Many bright stars, thick at center of round cluster, becoming less dense with distance from center.
Have a telescope? Point it to globular cluster Messier 3 on December 3, 2021, just before sunrise, and you will be able to see Comet C/2021 A1 (Leonard) just below this cluster on that date. Image from Adam Block/ Mount Lemmon SkyCenter.
Star chart with Arcturus and location of comet in tick marks.
Comet C/2021 A1 is traveling so fast that its position in our skies will change daily during early December 2021. Here is its location on December 5, 2021, about 90 minutes before sunrise. Comet Leonard will be located very close to where we see the bright star Arcturus, as seen in this chart. Facing east, as seen from U.S. Illustration by Eddie Irizarry using Stellarium.
Star chart with Arcturus and Spica and location of comet in tick marks.
Location of Comet C/2021 A1 (Leonard) on December 10, 2021. By then, it will be brighter but closer to the horizon, as seen from the U.S. about 30 minutes before sunrise. Illustration by Eddie Irizarry, using Stellarium.

Comet Leonard after sunset

Around December 14-16, 2021, Comet C/2021 A1 (Leonard) will become visible just after sunset, very low in the southwest horizon, as seen from the U.S.

Chart with Saturn, Venus, and tick marks for comet in twilit sky.
Location of Comet C/2021 A1 (Leonard) on December 15, 2021, about 30 minutes after sunset, facing southwest as seen from the U.S. Illustration by Eddie Irizarry using Stellarium.
Chart with Saturn, Venus, and tick marks for comet in twilit sky.
On December 17, 2021, about 30 minutes after sunset, comet Leonard will be located below planet Venus. Visible to the unaided eye? Perhaps …  Facing southwest, as seen from the U.S. Illustration by Eddie Irizarry using Stellarium.
Chart with Saturn, Venus, and tick marks for comet Leonard.
December 19, 2021, about 30 minutes after sunset.  facing southwest, as seen from U.S. Illustration by Eddie Irizarry using Stellarium.
Heliocentric chart of solar system showing trajectory of Comet Leonard.
This perspective on Comet C/2021 A1 (Leonard) shows its trajectory through our solar system. North is up. You can see that its orbit will cause it to be initially visible from Earth’s Northern Hemisphere, and then from the Southern Hemisphere. Chart via Dominic Ford’s In-the-Sky.

Comet Leonard photos from the EarthSky community

Submit your comet image to EarthSky

Telescopic view of a comet sliding near two galaxies.
View at EarthSky Community Photos | Radu Anghel in Parjol, Romania, captured this view of Comet C/2021 A1 Leonard with a 4-inch telescope on November 25, 2021, and wrote: “Comet C/2021 A1 Leonard sliding silently with galaxies NGC 4631 and 4656 on the background on the morning of 25 Nov.” Thank you, Radu!
Raymond Negron took this spectacular image of Comet Leonard passing almost in front of the Whale Galaxy (NGC4631) from San German, Puerto Rico on November 24, 2021. Thank you, Raymond!
Comet 67P shows greenish white comet head with whitish brown tail.
Brian Ottum captured this image of Comet 67P on November 10, 2021. Thank you, Brian!
Small fuzzy elongated green dot with long barely visible fuzzy tail in star field.
View at EarthSky Community Photos. | David Hoskin in Halifax, Nova Scotia, Canada, caught Comet Leonard on November 7, 2021 and wrote: “Comet Leonard (C/2021 A1) imaged this morning just before dawn. The comet is currently in Ursa Major and has an observed magnitude of 10.8, visible with a telescope aperture of 6″ or greater. The comet is predicted to brighten until 13 December, at which time it may be visible with binoculars.” Thank you, David!
Elongated fuzzy comet close to a distant galaxy with distinct spiral arms.
View at EarthSky Community Photos. | Eliot Herman in Mayhill, New Mexico, captured this photo of Comet Leonard and a spiral galaxy on October 30, 2021. He wrote: “Comet Leonard (C/2021 A1) is predicted to put on a nice show in a little more than a month. At present it is still faint at about magnitude 11, and on October 30 it had a very close conjunction with galaxy NGC 3897 in Ursa Major.” Thank you, Eliot!
Fuzzy green comet with short tail against distant star field.
Comet Leonard (C/2021 A1 Leonard) photographed on October 29, 2021, by Michael Jager (@komet123jager on Twitter) from Austria.

Bottom line: Comet C/2021 A1 (Leonard) – discovered on January 3, 2021 – is heading inward toward its January 3, 2022, perihelion. It still might become the brightest comet of 2021! Photos and charts here. Bookmark this post. We’ll be updating it.

Posted 
November 28, 2021
 in 
Astronomy Essentials

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