2024, September 30:  Comet Alert!

September 30, 2024:  Look for Comet Tsuchinshan-ATLAS during morning twilight from late September to early October.

(Sept. 22, 2024) --- Comet C2023-A3, or Tsuchinshan-ATLAS, was pictured about 99.4 million miles away from Earth by NASA astronaut Matthew Dominick using long-duration photography on a camera programmed for high sensitivity aboard the International Space Station
Photo Caption – (Sept. 22, 2024) — Comet C2023-A3, or Tsuchinshan-ATLAS, was pictured about 99.4 million miles away from Earth by NASA astronaut Matthew Dominick using long-duration photography on a camera programmed for high sensitivity aboard the International Space Station

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by Jeffrey L. Hunt

Comet Alert!

2024, September 30: Comet C/2023 A3 Tsuchinshan-ATLAS is visible before sunrise to the lunar crescent’s lower right. Use a binocular to see it.
2024, September 30: Comet C/2023 A3 Tsuchinshan-ATLAS is visible before sunrise to the lunar crescent’s lower right. Use a binocular to see it.

Comet C/2023 A3Tsuchinshan-ATLAS is visible before sunrise in the eastern sky. Find it low in the east-southeast below Leo, about 45 minutes before daybreak.  The thin crescent moon, nearly 15° above the east horizon, is 14° above the comet’s nucleus that is 5° above the horizon.

Comet Halley, 1986
Photo Caption – Comet Halley, 1986 (NASA Photo)

After a brief visit to the morning sky, it moves into the evening sky as the moon’s phase waxes and brightens next month.

Comets are frequent visitors to the inner solar system, where their icy masses are vaporized by the sun.  Most are unnoticed, except by experienced comet hunters and backyard enthusiasts.

Hairy Stars

The hairy stars are theorized to be the solar system’s primordial remnants.  They revolve around the sun in the Oort Cloud, thought to be at least 2,000 astronomical units (AU) from the sun and extending to 200,000 AU.  Earth’s distance is defined to be 1 AU.

This telescopic image from December 19, 2022, shows the brighter greenish coma, short broad dust tail, and long faint ion tail of Comet C/2022 E3 (ZTF). (Photo Credit: Dan Bartlett)
Photo Caption – This telescopic image from December 19, 2022, shows the brighter greenish coma, short broad dust tail, and long faint ion tail of Comet C/2022 E3 (ZTF). (Photo Credit: Dan Bartlett)

Their far-flung orbits are disturbed enough so that they begin a long plunge toward the sun.  On the way toward the central star, the dirty snowballs can be affected by Jupiter and Saturn’s gravity, changing their orbits.  Some are caught in orbits that carry them near the sun with periods of decades or centuries. Some fall into the sun’s fiery furnace.  Others pass closely to the sun and fracture into smaller pieces.

Comets’ Orbits

If unabated, the cometary mass begins to vaporize around Mars’ orbit and develop a bluish tail pushed away by the outward rushing solar wind, a stream of high-speed particles emitted by the sun.  Dislodged dust particles tail along the comet’s orbit, forming a second yellowish tail.

2024, September: Comet Tsuchinshan-ATLAS’s place in the solar system compared to the inner planets, Mercury, Venus, Earth, and Mars.
Chart Caption – 2024, September: Comet Tsuchinshan-ATLAS’s place in the solar system compared to the inner planets, Mercury, Venus, Earth, and Mars.

Unlike the moon and planets, many comets do not revolve around the sun in the plane of the solar system, making them visible anywhere in the sky. Comet Tsuchinshan-ATLAS’s orbit is tilted nearly 140° compared to the ecliptic and it revolves in the opposite direction from the planets.  It emerged from deep space above the solar system’s plane, passed perihelion, closest to the sun at a distance of 0.39 AU from the sun, about the same as Mercury’s solar distance, below the ecliptic plane.  It is heading out of the solar system moving north of the ecliptic again.

Sky watchers from the southern hemisphere are reporting very favorable views of the comet.  Recent predictions indicate that the comet could be very bright as it leaves the inner solar system.  We should be skeptical of predictions of a bright comet until it occurs.

A Comet Disappointment

Videographs of Comet Kohoutek taken by the 36-inch telescope at the Kitt Peak National Observatory on April 28, 1973 for the Skylab program
Photo Caption – Videographs of Comet Kohoutek taken by the 36-inch telescope at the Kitt Peak National Observatory on April 28, 1973 for the Skylab program

The most famous comet flop was Comet Kohoutek during early 1974.  It sprouted a small tail near Jupiter’s orbit.  In the popular press it was touted to be the brightest comet of the 20th Century.

The Comet Kohoutek book cover
Photo Caption – The Comet Kohoutek: Greatest Fiery Chariot of all Time book cover

Its brightness flopped and was barely visible.  The “Comet of the Century” spawned books and articles portending doom. 

A Wonderful Comet West

Comet West was discovered in photographs by Richard West on August 10, 1975. It reached peak brightness in March 1976. During its peak brightness, observers reported that it was bright enough to study during full daylight. Despite its spectacular appearance, it did't cause much expectation among the popular media. The comet has an estimated orbital period of 558,000 years.
Photo Caption – Comet West was discovered in photographs by Richard West on August 10, 1975. It reached peak brightness in March 1976. During its peak brightness, observers reported that it was bright enough to study during full daylight. Despite its spectacular appearance, it didn’t cause much expectation among the popular media. The comet has an estimated orbital period of 558,000 years. (Photo Credit: European Southern Observatory)

Two years later, Comet West was easily visible, but the public was not interested after the hyperbole of Kohoutek.

Not to downplay the possibilities of a spectacular comet this year, take a look for it with a binocular and hope for a bright display.  Otherwise, enjoy the view.

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