Well, it’s finally here! The week we’ve been anticipating for more than a year — the time when the great Comet Tsuchinshan-ATLAS (aka C/2023 A3) bursts spectacularly into view and becomes the long-awaited Comet of the Decade.
Or not.
Tsuchinshan-ATLAS was discovered on Jan. 9, 2023, by astronomers at the Purple Mountain Observatory in China.
Six weeks later it was found independently by South Africa’s Asteroid Terrestrial-impact Last Alert System.
Since then, the comet has been approaching the sun and just recently has rounded our star. It’s now heading back in our direction.
Some astronomers thought the comet might break apart during its close approach to the sun, so we’re all excited to see that it emerged unscathed and appears to be brightening faster than expected.
And that means that, when it reaches its closest to the Earth this week (officially on Oct. 12), it could become bright enough to see with the unaided eye at dusk.
Comet Tsuchinshan-ATLAS, like all others, is one of billions of tiny icy remnants of the primordial solar system that tumble silently through the vacuum of space.
Occasionally one of these cosmic nomads drifts inward toward the sun’s heat, and its ices disintegrate into a cloud of gas and dust around its nucleus (the “coma”).
Sunlight and the solar wind act as a fan and blow this material outward to create one or two tails that always point away from the sun.
As compact as a comet may appear to us from our perch on planet Earth, it is actually spread out over many tens of millions of miles; to achieve the density of the air we breathe, a comet’s entire tail would need to be compressed to fit into the size of an average suitcase.
In other words, a comet is the closest thing to nothing that’s still something!
Just how bright Tsuchinshan-ATLAS will appear as it passes us this week, however, is anyone’s guess.
Will it be bright enough to see with the unaided eye even before it gets dark, as some believe? Or will binoculars or a telescope be required just to find it in the glow of twilight?
No one can say for sure, since comets are notoriously fickle.
As noted comet-hunter David Levy likes to say: “Comets are like cats; they have tails, and they do precisely what they want.”
Either way, it may be possible to spot this interplanetary nomad in the early evening sky this week — if you’ve got a low, clear view of the western horizon.
Over the next week, Tsuchinshan-ATLAS will lie in the western sky shortly after sunset.
Be sure to use the accompanying illustration to help know where to look, but remember, the comet may not look like this at all.
Depending on how bright the comet is and how long its tail becomes, you may need binoculars to spot it lying somewhere between the star Arcturus and the brilliant planet Venus.
About all I can say with absolute certainty, however, is this: If you don’t head out this week at dusk to look, you will definitely miss the sky show.
Whatever that turns out to be!
