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.
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.
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.
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.
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.
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.
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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