A comet with potential to be brighter than Halley's will be visible beginning Saturday

John Meyer, The Denver Post on Oct 11, 2024

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Skygazers who have marveled at multiple displays of the northern lights in recent days have another reason to geek out over the next two weeks with the appearance of a comet in the western sky after sunset.

The comet C/2023 A3 Tsuchinshan-ATLAS should come into view for skygazers beginning Saturday evening around twilight. Astronomy experts say it should be visible for about two weeks, appearing slightly higher in the sky each night, and they believe it will be as bright as the brightest stars.

“Compared to Haley’s Comet, this one is supposed to be a lot brighter,” said Aislynn Mills of Mile High Astronomy, a store in Lakewood, Colorado, that sells binoculars, telescopes and other astronomy aids.

According to the astronomy site space.com, the head of the comet measures approximately 130,000 miles in diameter and the tail extends about 18 million miles. On a highly elliptical orbit, it rounded the sun this week and is making its way through the inner solar system back to outer space.

“The comet will practically vault into evening prominence during the middle of October,” according to the space.com post. “On Oct. 12, during mid-twilight (45 minutes after sunset), you will find Tsuchinshan–ATLAS approximately 6 degrees above the west-southwest horizon. Your clenched fist held at arm’s length measures 10 degrees in width, so the comet will stand about “one-half fist” above the horizon and will set (drop below the horizon) about 90 minutes after sunset.”

During the upcoming week, the post explains, A3’s apparent elevation over the horizon will increase by about 3 degrees each evening and set about 16 minutes later. It will generally follow the path the sun and moon take across the sky. By the end of next week, it should be “three fists” above the west-southwest horizon at “mid-twilight,” setting three and a half hours after sunset.

A comet is composed of a nucleus (core), a coma, a hydrogen “envelope” and two tails.

“The nucleus is the icy, rocky core — the physical thing that is traveling through space,” said Mills, who has an astrophysics degree from the University of Colorado. “As it approaches the sun, it’s sublimating that ice into gas, the (coma) we see around the nucleus. Then there is an invisible hydrogen envelope — hydrogen coming out around the coma — and the tails, an ion and dust trail.”

This comet takes its name because it was discovered in 2023 by the Tsuchinshan Observatory in China and the Asteroid Terrestial-impact Last Alert System (ATLAS). The latter was founded by NASA and operates at the Institute for Astronomy at the University of Hawaii, to detect objects that may impact Earth.

Don’t worry, though, this comet won’t.

Mile High Astronomy has posted a 28-minute video explaining comets as well as how to view and photograph them. If you’re looking for binoculars to help you see the comet, the staff there recommends choosing 7×50, meaning seven times magnification with a 50-millimeter front lens. The diameter of that lens determines the light gathering capability of the binocular. A 7×50 binocular, for example, has almost twice the light gathering ability of a 7×35 binocular.

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