Multiple bright outbursts have made Comet Leonard stunning photographically and visible without optical aid from southern locations. More disruptions are likely in store as it approaches perihelion.
Comet Leonard (C/2021 A1), which appeared to stall out around magnitude 5 in early December, has become a surprise performer. Since transitioning to the evening sky, it’s undergone three successive bright outbursts — on December 15th, 20th, and 23rd — that catapulted it to naked-eye visibility at 3rd magnitude. After each flare-up, the comet had faded back to around 4th magnitude. Today, December 25th, it’s around 3½. More outbursts are likely as Comet Leonard speeds toward perihelion inside the orbit of Venus on January 3rd and suffers the full brunt of the Sun’s heat.
Each flare began with a dramatic brightening of the comet’s “false nucleus” — a bright starlike concentration within the coma. Amateur astronomer Piqui Diaz of Ezeiza, Argentina, noted a condensed but hazy coma on December 19.01 UT, but one night later, the comet’s appearance caught her completely off guard. Expecting to see a fuzzy glow, the coma instead looked like a bright “star” in her 90-mm refractor. The cause of each outburst is likely due to vaporization of fresh, dust-laden ice from solar heating as the comet dashes sunward.
Comet Leonard currently glows around magnitude 4 and hovers very low in the southwestern sky an hour to 75 minutes after sunset for North American skywatchers. Its altitude depends upon your latitude. From the southern U.S. the comet perches a reasonable 10° to 12° high at mid-twilight and may be faintly visible with the naked eye. But if you live in the northern half of the country, it practically scrapes the horizon with an altitude of just 3° to 5°. You’ll need transparent skies, an unobstructed horizon, and binoculars or a small telescope to see it.
You’ll also need to know exactly where to look, and there are few bright stars to guide you there. But don’t despair. Using the planets to make triangles that included the comet at one apex, I spotted the fuzzy blob in binoculars from Duluth, Minnesota (latitude 47° north) on both December 20th and 24th. The camera did better, showing it more clearly than I could see with my eyes. Given the comet’s southern declination, Southern Hemisphere observers have the best view, with this celestial visitor standing 20° (and climbing) 90 minutes after sunset from mid-southern latitudes.
If you’re struggling to find the comet, take a photo of where it’s supposed to be. That’s what worked best for me. When it pops up on your display (replay) screen, you’ll know exactly where to point your telescope or binoculars.
Comet Leonard’s ion tail has shown remarkable complexity that you can see for yourself in breathtaking images taken by Austrian astrophotographer Michael Jäger and others. Continuous changes in tail length, along with the appearance of streamers, kinks, and knots, show just how captivating and unpredictable comets can be. And all this from a kilometer-wide berg of dirty ice. Miracles of nature never cease.