A comet named C/2021 A1 (Leonard) is predicted to brighten enough to see with unaided eyes in mid-December, when it will appear in the eastern sky before sunrise. The comet was discovered by G. J. Leonard at the Mount Lemmon Observatory on January 3, 2021, when the comet was 5 AU (or 750 million kilometres) from the Sun.
For now, the comet is shining around magnitude 8, well within reach of backyard telescopes from a dark location and possibly larger binoculars. This week, the comet will rise at about 12:30 a.m. local time and then climb the eastern sky until dawn. For the next week, Comet Leonard will be located above (or celestial northwest of) the very bright star Arcturus.
Comets move rather quickly compared to the background stars. This week, it will traverse 1.4 fist diameters — or 14 degrees of sky — more or less toward Arcturus.
In the pre-dawn sky from Monday to Friday, the comet will be moving along the border between Canes Venatici (the Hunting Dogs) and Coma Berenices (Berenice’s Hair). On the coming weekend, it will enter Boötes (the Herdsman). The waning crescent Moon will share the morning sky with it until about Friday.
Comet viewing tips
If your location is dark, try seeing the comet in binoculars, especially later in the week. It should resemble a faint fuzzy patch or unfocused star. Look for its fainter tail extending roughly upwards (i.e. pointed away from the horizon). In a telescope, you may see a faint hint of green. Always begin with your lowest-power eyepiece. If you use Stellarium or an app, you should update the orbital elements for solar system objects so that the comet’s position is plotted correctly. Then use the app’s flip buttons to show the same orientation that your telescope produces, and find the star patterns that should be surrounding the comet. Finally, if you aren’t seeing it yet, try tapping the telescope while you are looking. Making a faint fuzzy object “dance” a little will make it more visible.
On the morning of Friday, December 3, Comet Leonard will pass very close to the bright globular star cluster named Messier 3 in Canes Venatici. Both objects should be bright enough to see in binoculars from dark sky locations, and will be telescope-close for several hours. On the following night, the comet will pass the fainter globular cluster NGC 5466, also known as the Snowglobe Cluster.
The comet should brighten every morning as it nears the warmth of the Sun. But it will also be shifting closer to the Sun in the sky by descending toward the horizon. By the time we get to the predicted peak brightness next week, it will be rising closer to sunrise. That means it will sit lower and shine through a thicker layer of Earth’s distorting atmosphere, in a brightening sky. So look sooner than later! And, once you’ve successfully found and seen it, it will be easy to do that again each consecutive morning.
Comet Leonard will pass the Sun and enter the evening sky after mid-December, but it won’t climb far above the western horizon. And there’s no guarantee that it will survive as it nears perihelion on January 3, 2022. So check the weather forecast and set the alarm!
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the Universe together.