Astronomy Essentials

Comet Leonard, and its glorious sweep past M3

Astrophotographer Greg Hogan in Kathleen, Georgia captured the video above. He said it shows about an hour’s movement of the comet, in relationship to M3. Also see his beautiful single exposure, here.

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. The comet is currently heading sunward, toward its perihelion (closest point to the sun) on January 3, 2022. Comets are typically brightest around perihelion. Comet Leonard has been in the morning sky, and it just passed the beautiful globular star cluster M3. See the photos on this page, and view more at EarthSky Community Photos. This month, Comet Leonard will become visible in the evening sky. All in all, it’s time to look for a comet!

Astronomer Greg Leonard discovered the comet as 2021 began. Discovery images already 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.

Over the coming month, as Comet Leonard heads sunward, it’ll sweep closest to Earth on December 12. It won’t be particularly close at its closest, passing more than 21 million miles (34 million km) away. But six 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 on November 28:

The current estimated magnitude [brightness] of Comet Leonard (C/2021 A1) is 10.64 (JPL) while the latest observed magnitude is 7.5 (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.

EarthSky 2022 lunar calendars now available!  They make great gifts. Order now. Going fast!

Comet and globular star cluster.
View at EarthSky Community Photos. | On December 3, 2021, comet C/2021 A1 (Leonard) was near in the sky to the stunning globular star cluster Messier 3. Patrick Prokop in Savannah, Georgia, wrote: “Comet Leonard and M3. This is a composite of 30 x 2-minute exposures. Here you can see comet Leonard passing the beautiful cluster that contains a bit more than 500,000 stars and is about 33,900 light-years away. The age of the majority of stars is roughly 8 billion years old, as compared to 4.6 billion years of our sun. The comet is only about 40,000 miles from Earth and is moving at a velocity of around 37.6 miles/sec [60.5 km/sec] or 99,500 mph. I took this image between 5-6 a.m., Friday, December 3, 2021, using the Orion EON 130mm refractor telescope.” Thank you, Patrick! See more Comet Leonard photos at EarthSky Community Photos.
Comet and globular star cluster.
View at EarthSky Community Photos. | Chris Woodruff in Lockwood Valley, California, also captured the comet and M3 on December 3, 2021. Chris wrote: “Woke up this morning at around 4:30 a.m. PST in Valencia, California. I logged into my remote observatory in the Lockwood Valley and captured a set of 240-sec, 140-sec, and 60-sec images using my Radian 61 f/4.5 Imaging APO Telescope with an SBIG 8300c camera. Was very surprised to see how close these objects were (using your website as a guide). This is the first quick process using only the 240-sec images but will see if combining all of the images will give a bit more detail once I get a chance.” Beautiful, Chris! Thank you. See more Comet Leonard photos at EarthSky Community Photos.

Will you see Comet Leonard?

Will the comet get bright enough to see with the eye alone in December? It’s possible that Comet Leonard might reach 4th magnitude before its early January perihelion. But 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, possibly glimpse-able with the eye alone. It would be fun to try to see and even more fun to spot it!

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

Remember, you need a dark sky. And you’ll need a pair of binoculars … ordinary 10×50 binoculars from a discount store is a reasonable way to go.

If you do see it, it’ll look like a fuzzy star.

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

By that we mean that this comet takes tens of thousands of years to complete an orbit around the sun. As Bob King pointed out at 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, you or I won’t see Comet Leonard again.

Ultrafast comet

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. Is it possible to observe this comet’s motion. Yes, if you’re a careful observer and willing to spend some time. The best way would be with a small telescope. You’d do it by taking a close look at the comet’s position relative to background stars. Then compare the telescopic view five or 10 minutes later to detect the comet’s motion. Despite its high speed, you’ll find that its distance from Earth – and the vast distances in our solar system – will cause the comet to appear as a very slow-moving object.

Here are a few charts …

Comet Leonard before sunrise

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 The Sky Live.

Comet Leonard photos from the EarthSky community

Submit your comet image to EarthSky

Comet Leonard: Green comet with small, oblong white core surrounded by fuzzy green, and 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.
Green fuzzy comet with long tail near two elongated smudges in a starfield.
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!
Bright green fuzzy comet with tail crossing longish smudge with bulge in the center.
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!
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.

December 4, 2021
Astronomy Essentials

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