It’s uncommon to see a comet at its finest: Most comets are brightest nearest the solar, simply once they’re most tough to identify in opposition to the solar’s glare or hidden under the horizon.
Comet C/2021 A1 (Leonard) is, alas, no exception. But it surely needs to be seen in small telescopes and binoculars and fairly probably even dimly to the unaided eye within the Northern Hemisphere’s pre-dawn sky because it will increase in brightness for at a part of December, and later within the month maybe even briefly within the night sky, simply after sundown.
Astronomer Gregory J. Leonard, a senior analysis specialist, found the comet that now bears his identify on Jan. 3 on the Mount Lemmon Infrared Observatory, situated within the Santa Catalina Mountains, roughly 17 miles northeast of Tucson, Arizona.
Associated: Evening sky, December 2021: What you’ll be able to see this month [maps]
Since its discovery, the comet has been approaching each the solar and Earth however has been a really dim object. Most comets stay too faint for novice telescopes to catch, however for a short time in December, Comet Leonard ought to rise out of the peculiar.
The icy ball has come an extended approach to make this pre-Christmas look to us. About 35,000 years in the past, the comet was on the far finish of its elongated elliptical orbit — aphelion — some 3,500 astronomical items from the solar. One astronomical unit (AU) is the equal of the Earth’s common distance from the solar: 92,955,807 miles (149,565,894 kilometers).
So, 35 millennia in the past, Comet Leonard resided some 325 billion miles (525 billion km) from the solar, enveloped in an nearly unimaginably chilly surroundings, hovering only a fraction of a level above absolute zero, the temperature at which all molecular movement stops. Now, Comet Leonard is within the house stretch of what doubtless shall be its final go to to the solar, and its conglomeration of icy gases like methane, ammonia and water vapor is reacting to the rising heat of the solar.
December is Leonard’s month
Comet Leonard’s brightness ought to noticeably ramp up because it approaches the Earth. Within the early days of December, observers who’re up across the break of daybreak (roughly 5:30 a.m. native time), ought to think about the japanese sky about midway up from the horizon to the purpose straight overhead. Now, with binoculars, scan that a part of the sky roughly halfway between the Third-magnitude star Cor Caroli within the constellation Canes Venatici (the Looking Canine) and the Third-magnitude star Muphrid within the prolonged foot of Boötes the Herdsman.
There, it is best to run throughout a round, fuzzy, Sixth-magnitude glow maybe sporting a tail. That shall be Comet Leonard.
For many of us, the second week of December is when Comet Leonard needs to be most fascinating, providing one of the best compromise between rising brightness and lowering altitude initially of daybreak. Furthermore, the sky shall be freed from moonlight, as it is going to be shortly after the new moon of Dec. 4.
On the morning of Dec. 6, about two hours earlier than dawn, look towards the japanese sky. You’ll instantly discover the sensible orange-yellow star, Arcturus within the constellation of Boötes the Herdsman. Now, with binoculars, scan that a part of the sky about 5 levels to the left of Arcturus and it is best to see Comet Leonard. The comet’s mud tail, which began to elongate noticeably throughout early November, needs to be pointing nearly straight up.
The comet’s magnitude is forecast to be +5.5; shiny sufficient to be glimpsed with none optical support in a darkish sky free of sunshine air pollution. The comet will then be 31.9 million miles (51 million km) from Earth and approaching us by about 1.5 million miles (2.4 million km) per day, so it is going to be brightening noticeably, however it should additionally drop quickly decrease within the japanese sky with every passing day.
By the morning of Dec. 12, Comet Leonard can have brightened to magnitude +4.3, however shall be solely 10 levels above the japanese horizon initially of morning twilight. (Your clenched fist at arm’s size measures roughly 10 levels.) In accordance with NASA’s Jet Propulsion Laboratory in California, the comet shall be making its closest strategy to Earth that very same day, reaching simply 21,687,279 miles (34,902,292 km) away at 10:54 a.m. EST (1354 GMT).
That day will mark the top of its morning visibility, however Comet Leonard will return for a number of “cameo appearances” within the night sky. On Dec. 17, it is going to be sliding 5° under dazzling Venus. With binoculars, search for it very low towards the southwest horizon about an hour after sundown.
Ahead scatter may enhance visibility
Some skywatchers are hoping that the comet will over-perform by way of brightness expectations, as a consequence of a phenomenon referred to as “ahead scatter.” In such a scenario, a back-lit comet can seem considerably brighter as a result of the mud and ice crystals emanating from the comet’s nucleus scatter mild towards the observer.
In the course of the center a part of December, Comet Leonard shall be at a really favorable part angle relative to the solar and Earth, suggesting that it’d get 1 to 2 magnitudes brighter than what present predictions counsel; put one other approach, the comet may exceed brightness estimates by 2.5 to six.3 instances. Comets which have benefited from ahead scattering embrace Skjellerup-Maristany in 1927, West in 1976, Bradfield in 1980 and McNaught in 2007. All 4 comets surged in brightness and have become a lot brighter than anticipated.
Not all comets react favorably to forward-scattering, nevertheless. Will Comet Leonard profit? We are able to solely watch and see what occurs.
The comet will doubtless be misplaced to view after Christmas, reaching its closest level to the solar on Jan. 3 at a distance of 57.2 million miles (92 million km). As soon as it rounds the solar it is going to be thrown out of the photo voltaic system right into a barely hyperbolic orbit, by no means to be seen once more.
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Joe Rao serves as an teacher and visitor lecturer at New York’s Hayden Planetarium. He writes about astronomy for Pure Historical past journal, the Farmers’ Almanac and different publications. Comply with us on Twitter @Spacedotcom and on Fb.