Comet Tsuchinshan-ATLAS Climbs, Brightens and Delights!

Rising from the solar fire, Comet Tsuchinshan-ATLAS (C/2023 A3) triumphantly returned at dusk on October 11th after intense anticipation by amateur astronomers and the public alike. That evening, I drove 15 miles north of home and methodically swept the sky to the right of Venus with binoculars. Exactly 40 minutes after sunset I stopped — there it was! The comet exhibited a tiny, bright coma and a ghostly tail that showed up best in short time exposures with a telephoto lens. Despite excellent sky conditions I saw nothing with the unaided eye.

But just one night later, the comet’s altitude had risen sufficiently that many observers had no problem seeing it without optical aid. Through binoculars the tail grew to 7°. Both single and stacked images revealed rays within the tail and the first signs of the antitail below the comet’s head. Already the antitail has narrowed dramatically (as of October 14th) and should continue to mimic a laser beam on Tuesday night, October 15th, as Earth crosses through C/2023 A3’s orbital plane.

Even before C/2023 A3 slipped back into the evening sky we watched its progress across the LASCO C3 coronagraph on the orbiting Solar and Heliospheric Observatory (SOHO). The comet’s head arrived first, followed by a bright and brilliant dust tail set aglow by forward-scattered sunlight. The combination dust-and-anti-tail extends for at least 50°!

Altitude makes a big difference in being able to trace the full breadth of a comet’s tail(s), and we’ll have that in spades in the next few weeks as this feathery gem climbs the southwestern sky rung by rung, gaining about ~3° elevation per night. On October 11th when I first spotted the comet at dusk, I needed binoculars to identify it. Two nights later, after it had climbed an additional 7°, not only was the head visible but 5° of tail, too. On October 14th it was a feather of light in the west with a 10° tail visible even in bright moonlight.

Parting is such sweet sorrow

The comet is currently visible in the western sky about 2½ fists to the upper right of Venus and dimly visible with the naked eye and binoculars as soon as 45 minutes after local sunset. You’ll see it best between 1 and 2 hours after sunset as the sky gets darker. Use this sunrise-sunset calculator to determine when the Sun sets at your location.

C/2023 A3 will slowly fade as it departs Earth’s vicinity, traveling faster than 195,000 kilometers per hour on October 15th. Moonlight has been and will continue to be an issue until about October 20th when we’ll see the comet again in a dark sky with the Moon three days past full. On that date it should glow at 3rd magnitude, sport both ion and dust tails, and make a splendid naked-eye sight from the countryside. Although it will have dimmed to 6th magnitude by Halloween, rural observers might still glimpse it. The rest of us should easily spot it in binoculars.

This snowball from the cold version of hell will be with us for some time. Even as its brightness takes a slow tumble, the comet will keep a light on for ardent observers, glowing at around magnitude 10.5 in Aquila at year’s end. We’ll see it fade, shrink, and lose its tail as it returns to deep space. Although C/2023 A3’s orbital parameters are still in flux, it will likely not return for millions of years.

Having watched Comet Tsuchinshan-ATLAS evolve from a 13th-magnitude fuzzball last winter into the bright and elegant object that now adorns the evening sky fills me with gratitude. Most comets don’t become easy naked-eye objects, making this a precious opportunity for amateurs to witness the myriad facets of a comet’s “life” cycle.

Enjoy these additional images. You’ll find many more in the Comet Watch and ICQ Comet Observations Facebook groups.