2023, January 22-29: Comet Alert!

January 22-29, 2023:  A comet is visible through a binocular during the next week all night in the far northern sky moving from night to night between the Dippers.

2023, January 22-29: Comet C/2022 E3 (ZTF) is shown between the Big Dipper and Little Dipper at an hour after sunset.
Chart Caption – 2023, January 22-29: Comet C/2022 E3 (ZTF) is shown between the Big Dipper and Little Dipper at an hour after sunset.

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by Jeffrey L. Hunt

Comet C/2022 E3 (ZTF) is visible through a binocular during the next week as it moves in the far northern sky between the Big Dipper and Little Dipper.

The chart above shows the comet an hour after sundown.  At this far northerly location, the “hairy star” is visible all night.  It rises higher in the sky as midnight approaches.  By the time morning twilight begins, it is high in the north. The comet does not set from the mid-northern latitudes.  It can be seen at all nighttime hours.

Unlike the planets, this comet moves at a highly inclined orbit compared to the solar system’s plane, so it passes through the far northern sky.

Comet NEOWISE, July 13, 2020
Photo Caption – 2020, July 13: Comet NEOWISE (Comet C/2020 F3 NEOWISE) appears above the northeast horizon during early morning twilight.

In a very dark location, free from all outdoor lighting, the comet may be visible to the unaided eye, but it is best viewed through a binocular.  A good test for the darkness of the view is the ability to see all of the Little Dipper’s stars.  If the four stars between Polaris and the “Guardian Stars,” Pherkad and Kochab, are visible, the comet might be seen without an optical assist.

During the next week, it moves mainly through Draco, passing the Guardians on the 26th and 27th.  The moon grows brighter during the evening hours, setting around midnight on the 28th.  As the moon brightens, shift the view to about 90 minutes before sunup, away from moonlight and an early alarm.

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)

A comet is a frozen concoction of gasses – water, methane, ammonia, and others – and dust.  Liquids cannot exist in space, so when the icy mass nears the sun, the ices vaporize, forming a fuzzy appearing coma around the central cometary nucleus.  The solar wind – high speed particles that stream away from the sun – drives the dust and gasses away forming a dust tail and a separate ion tail.

In the past comets brought with them connotations of doom and gloom. Witnessing a comet in the night sky could very well be one of the scariest things a person might see up there in the heavens. Nowadays, given sufficient distance from the Earth, comets elicit a distinctly different reaction. People gaze at them in wonder from even bright city skies- and amateur astronomers enjoy the change in pace from their usual astronomical vistas. This comet, Machholz (C/2004 Q2), rounded the Sun in 2005 and is now on its journey to the outer part of the solar system. On its way, people in the northern hemisphere could catch a glimpse of it during early 2005. This image was taken as part of Advanced Observing Program (AOP) program during 2014 at Kitt Peak Visitor Center.
Photo Caption – This comet, Machholz (C/2004 Q2), rounded the Sun in 2005 and is now on its journey to the outer part of the solar system. (Photo Credit: Kitt Peak National Observatory)

Comets are usually named for their original discoverers.  Comet Halley was named for Edmund Halley who first predicted the return of a comet that visited previously.  Since then, professional astronomers and die-hard amateur comet hunters have their names in history from their first observations of comets.

Sunset image of the Hale 200-inch Telescope dome with the rising nearly-full moon.
Photo Caption – Sunset image of the Hale 200-inch Telescope dome with the rising nearly-full moon. (Palomar/Caltech)

Today automated systems on satellites and terrestrial telescopes frequently scoop the discovery of a new comet and the name, removing the romance of tireless observing at the telescopic eyepiece.  This comet has the letters ZTF, for the Zwicky Transient Facility that is on the campus of the famous 200-inch telescope at Mount Palomar, California.  The ZTF’s wide-field camera system can photograph the entire northern sky about every two days to quickly capture changes, such as cometary motions, never-charted asteroids, and activity in distant galaxies.

Comet C/2022 E3 (ZTF) was first reported by Palomar as a possible asteroid or minor planet during early March 2022.  Subsequent detailed photographs by Japanese astronomer Hirohisa Sato indicated the body’s coma.  Others reported a coma and a tail.

An orbit was calculated during the next month from multiple observations.  Once the predicted orbital path was known, the comet’s place in the starfield, known as an ephemeris, was calculated.

From the comet’s calculated orbit and its long orbital period, it is suspected to be from the Oort cloud, a theoretical spherical repository of small frozen masses that revolve around the sun.  The precise distance and thickness of the shell is unknown, but thought to start around 2,000 times the Earth’s distance from the sun and range to 100,000 times the distance.  The farthest edge may reach about one-fourth of the way toward the nearest star.

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)

Something in the outer reaches of the solar system, must disturb the cometary mass enough so that its orbit changes, plunging toward the sun. The comet may have started falling from the cold swarm tens of thousands of years ago.

The gravitational influence of the planets, especially Jupiter can trap comets in smaller orbits that carry the comets past the sun frequently.  This year over 30 short-period comets pass closely to the sun and develop their characteristic comas and tails.

Jupiter’s gravitational influences may have placed comets on collision courses with Mercury, Venus, Earth and Mars.  Some have hypothesized that a rain of comets brought water to Earth early in the solar system’s history.

A comet’s brightness is difficult to predict.  It may become brighter during the week, but not likely into easy visual range.

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