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.
Since its discovery by Astronomer Greg Leonard in January 2021, the comet has been approaching both the sun and Earth but has been a very dim object. And Leonard has come a very long way to make its pre-Christmas appearance.
According to Space.com, about 35,000 years ago, the comet was at the far end of its elongated elliptical orbit — or aphelion — some 3,500 astronomical units from the sun. One astronomical unit (AU) is the equivalent of the Earth’s average distance from the sun: 92,955,807 miles (149,565,894 kilometers).
So, this means that 35 millennia ago, Comet Leonard resided some 325 billion miles (525 billion kilometers) from the sun, enveloped in an almost unimaginably cold environment, hovering just a fraction of a degree above absolute zero, the temperature at which all molecular motion stops.
Now, Comet Leonard is in the home stretch of what likely will be its very last visit to the sun, and its conglomeration of icy gases like methane, ammonia, and water vapor is reacting to the increasing warmth of the sun.
December is Leonard’s month to shine
Although comets are notoriously hard to predict, according to NASA, some estimations have Comet Leonard brightening to become visible to the unaided eye in the second week in December.
On the morning of Dec. 6, about two hours before sunrise, look toward the eastern sky. You will immediately notice the brilliant orange-yellow star, Arcturus in the constellation of Boötes the Herdsman.
A simple way of finding the constellation is to look along the handle of the Big Dipper away from its spout, arcing to the bright orange star Arcturus, forming the base of the constellation Boötes, which may look like a kite to some people.
Using an inexpensive pair of ordinary 10×50 binoculars, scan part of the sky about 5 degrees to the left of Arcturus and you should see Comet Leonard. The comet’s dust tail, which started to lengthen noticeably during early November, should be pointing almost straight up.
December 12 will mark the end of its morning visibility, but Comet Leonard will return for several “cameo appearances” in the evening sky. On Dec. 17, it will be sliding 5° below dazzling Venus. With binoculars, look for it very low toward the southwest horizon about an hour after sunset.
