A celestial spectacle not seen since the Stone Age is gracing our night skies, offering stargazers a once-in-a-lifetime opportunity. Comet Tsuchinshan-ATLAS, also known as C/2023 A3 or simply Comet A3, has emerged as one of the most impressive naked-eye comets this year.
As the sun dips below the horizon on Tuesday evening, October 15, sky enthusiasts are poised for a treat. It marks the second of two prime viewing opportunities for northern hemisphere observers to witness this cosmic visitor at its brightest.
How Long Will the Comet Be Visible For?
Comet A3 will technically be visible into late October, but its brightness is diminishing each day as it heads away from Earth. So, getting out on Tuesday night offers your best chance of viewing it.
The comet reached its closest approach to Earth on Saturday, at a dizzying 44 million miles away. However, it was tricky to spot as it remained close to the sun.
Its perihelion—the closest point to the sun—occurred on September 27, according to EarthSky. After rounding the sun, comets are often brighter, with longer tails, as the heat from the sun vaporizes ice from the surface, sending it off into space.
How Fast Is the Comet Moving?
Comets move fast. Really fast. According to data from NASA's Jet Propulsion Laboratory, the maximum orbital speed of Comet A3 is a whopping 150,000 miles per hour.
The comet reached its top speed when it was closest to the sun, as our star exerts the maximal gravitational pull on the dirty snowball.
As it moves away from the sun, the comet will slow down somewhat, but will still be moving at a considerable pace. Despite this, the orbital period of Comet A3 is 80,000 years. That's because it has an awfully long way to travel—out to the Oort Cloud, a minimum of 2,000 astronomical units (AU) away from the sun. For context, one AU is about 93 million miles.
Where To Look for the Comet Tonight
To catch a glimpse of our celestial guest, you'll need to look west around 45 minutes after sunset where you're located. The comet will be about 46 million miles from Earth and should be visible just above the western horizon.
The comet will set around hour and 40 minutes after it first becomes visible.
As the moon is nearly full on Tuesday, the sky will be a little brighter, which can make the comet harder to see. That said, the moon should be shining in the southern portion of the sky, so it shouldn't interfere too much with the viewing spectacle.
You'll need clear skies to view the comet, so check your local weather forecast to see whether you're in with a shot.
How to See Comet A3 Tonight
The comet will have a magnitude +0.9 tonight, according to Forbes, meaning it will be visible to the naked eye. For reference, the north star has a magnitude of around 2, meaning the comet is more than twice as bright as the famous celestial compass point.
For the best viewing, use a pair of binoculars or, if you're lucky enough to have one, a telescope.
Finding high ground will keep the comet above the horizon for longer, and going to a dark spot away from the light pollution of city lights will help too.
What is a Comet?
Comets are icy remnants from the early days of our solar system, composed of dust, rock, and frozen gases. While often imagined as fiery objects streaking across the sky, comets only develop their iconic glowing tails when they venture close to the sun.
As they near the sun, the heat causes their ices to vaporize, releasing gas and dust that form a glowing coma and a long tail that can stretch millions of miles into space.
In their original state, before heating up, comets can range in size from just a few miles to tens of miles across. But once their materials start to sublimate and expand near the sun, they can appear larger than most planets.
NASA estimates that there are billions of comets orbiting in the Kuiper Belt, a region of icy objects beyond Neptune, and even farther out in the Oort Cloud, which is home to the most distant and ancient objects like Comet A3.
New comets are discovered every year. However, many either burn up when they get too close to the sun or remain too distant to be seen without specialized telescopes.
Some well-known comets from recent history include Neowise in 2020 and Hale-Bopp and Hyakutake in the 1990s. In 2023, a rare green comet that hadn't visited Earth in 50,000 years made a close pass by our planet, offering a stunning spectacle for skywatchers.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about comets? Let us know via science@newsweek.com.
Disclaimer: The copyright of this article belongs to the original author. Reposting this article is solely for the purpose of information dissemination and does not constitute any investment advice. If there is any infringement, please contact us immediately. We will make corrections or deletions as necessary. Thank you.
