What started as a tiny smudge of light near Jupiter in early 2021 became the brightest comet of the year as we near January once again. And now is precisely prime time for viewing this celestial visitor from afar as it makes its pre-Christmas Earth appearance along its parade route to the Sun.
This ball of frozen gas and dust, with its white oblong core, emits a marvelous greenish glow and a signature comet tail. As it is increasingly warmed by the Sun’s light, the amorphous, fuzzy object sheds its vapor across the solar system like lingering fireworks.
For a few more days—particularly in this second week of December—the comet’s brightness will ramp up noticeably and may be seen using binoculars, a telescope, or maybe even with the naked eye in the pre-dawn sky. During this period, at around 5:30 a.m., according to Space.com, the comet—cumbersomely dubbed “C/2021 A1 Leonard” or simply “Comet Leonard”—will appear near the horizon in the vicinity of the star Arcturus.
The Discovery of Comet Leonard
“C/2021 A1 Leonard” garnered its unwieldy name from University of Arizona astronomer Greg J. Leonard, who on Jan. 3, 2021, first spotted the dim object. It was barely visible, heading inbound toward the Sun at a breakneck speed of 158,084 miles per hour (254,412 km/h)—a mind-blowing 43.91 miles per second (70.67 km/s), according to EarthSky. That’s fast, but such speeds are minuscule amid the vast celestial backdrop of space, planets, and stars, where distances are measured in millions of miles or light-years.
At that speed, it will sweep closest to Earth by Dec. 12, though it won’t be particularly close at a distance of over 21 million miles (34 million km) away. Nor will it be particularly visible by Dec. 12, appearing too low on the horizon for many living in the Northern Hemisphere to glimpse. From there, Comet Leonard will continue on its Sun-destined journey.
Where’s It Going? Where’s It Been?
Exactly one year after its initial sighting, Comet Leonard on Jan. 3, 2022 will reach its perihelion (closest distance from the Sun along an elliptical orbit)—though that’s still a span of 57.2 million miles (92 million km). At which point, viewing will be pointless against the Sun’s mighty glare, despite the comet’s then reaching peak brightness. And as quickly as it came, so will C/2021 A1 Leonard swoop around the Sun along its parabola-like path, disappearing into deep space, (probably) never to return.
About 35,000 years ago, that icy conglomeration of methane, ammonia, and water was at its farthest point from the Sun (its aphelion)—some 3,500 astronomical units away (about 325 billion miles); temperatures in deep space hover just a fraction of a degree above absolute zero (where no molecular movement is present at all). But as Leonard’s comet drew near our system, increased energy levels from our Sun led to its shedding dust and gasses across our galaxy, causing the super-bright spectacle currently on display.
As for the cause of the comet’s green tinge? NASA explains that the comet’s coma–the nebulous matter surrounding its core, or nucleus–contains a poisonous gas called cyanogen as well as diatomic carbon, both of which glow green when illuminated by sunlight. The green fireworks display also signals that it’s getting more active as it approaches the Sun.
Comets are notoriously unpredictable as to what brightness (magnitude) they will yield. With a forecasted magnitude of +4.3, according to Space.com (within the naked eye limit, which could still increase by orders of magnitudes by mid-December), Comet Leonard hasn’t disappointed stargazers in the least—it’s expected to get better. But don’t miss your chance! Dec. 12 will mark the end of the comet’s morning visibility, returning for a brief encore during evenings from Dec. 15 below the planet Venus.
New Year’s 2022 will herald the end of this epically climactic 2021 cosmic fireworks show.