7:15 AM | *Comet Leonard makes its closest approach to Earth on Sunday...could be seen in the early morning sky next few days...comet transitions to the early evening sky around December 14th*
Paul Dorian
Photograph of Comet Leonard was taken on Tuesday, December 7th in southern Finland using an DSLR camera (photo courtesy Spaceweather.com)
Overview
Comet Leonard is rapidly brightening as it approaches Earth for its closest approach on Sunday, December 12th (35 million kilometers). The comet has now reached the “6th magnitude” brightness level and is visible (barely) to the unaided eye. Between now and Sunday, December 12th, the comet could brighten another 5-fold to magnitude +4 according to spaceweather.com. If the weather cooperates, Friday, Saturday and Sunday mornings may be the best bets for viewing at around 6am in the eastern sky. On Monday, the comet will disappear from northern hemisphere viewers, but then return later next week in the early evening sky, as it heads towards the sun. Comet Leonard will reach perihelion - its closest point to the sun - on January 3rd, 2022.
The blue curve traces the predicted brightness of Comet Leonard back to August 2021 with “crosses” showing recent observations. Credit: Spaceweather.com; Comet Observation Database
Discussion
Astronomer Greg Leonard discovered the comet that now bears his name in early January of this year while viewing the skies at the Mount Lemmon Observatory in Arizona. (By the way, Greg Leonard has discovered 13 comets, but is most excited about this one because of “how visible it will be”). Comet Leonard officially known as “C2021/A1” is now visible (albeit barely) to the naked eye as the comet heads towards its closest approach to the Earth which will occur this Sunday, December 12th at some 35 million kilometers away. If the unaided eye doesn’t work (i.e., if not in a dark enough region), small backyard telescopes and binoculars should have no trouble finding Comet Leonard over the next few mornings in the pre-dawn sky. Around December 14th, the comet will transition to the early evening sky as it continues on its way towards the sun. As the comet approaches the sun in early January, 2022, forward scattering of sunlight through its dusty atmosphere could create an additional surge in brightness according to spaceweather.com. Comets are typically brightest around the time they’re closest to the sun.
This map of the sky at 6 a.m. shows where to look for Comet Leonard during the next few mornings. It is based on a diagram created with the software known as “Stellarium”. (Courtesy Canadian Broadcasting Corporation/Chris Vaughan)
An amazing feature of Comet Leonard is that it’s an ultrafast comet according to EarthSky.org. It’s traveling at 158,084 miles per hour (254,412 km/h or 70.67 km per 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.
Location of Comet C/2021 A1 (Leonard) on Wednesday, December 15, 2021, about 30 minutes after sunset, facing southwest as seen from the U.S. Illustration by Eddie Irizarry using Stellarium software. Courtesy EarthSky.
Viewing Comet Leonard is truly a “once-in-a-lifetime” opportunity as it is not expected to ever pass this way again. The comet formed about 4.5 billion years ago and comes from about 550 billion kilometers away, or 3,700 times the distance between the sun and the Earth. According to astronomer Greg Leonard, "it's been inbound toward the inner solar system for the past 35,000 years. It's zooming through space at 70 kilometers per second, that's enough speed for it to get flung away from our solar system." In other words, it may arrive in some other star system millions and millions of years from now.
Meteorologist Paul Dorian