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.
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
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.
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.
Eddie Irizarry of the Sociedad de Astronomía del Caribe (Astronomical Society of the Caribbean) has been a NASA Solar System Ambassador since 2004. He loves public outreach and has published multiple astronomy articles for EarthSky, as well as for newspapers in Puerto Rico. He has also offered dozens of conferences related to asteroids and comets at the Arecibo Observatory.
Asteroid 33012EddieIrizarry, a 7.8 km space rock, has been named in his honor.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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