7.2 million miles away and we "might" be able to see it
The Comet 46P/Wirtanen will have a "close" encounter with Earth on Sunday, Dec. 16. As with all objects in space,
is a relative term.
Comet 46P/Wirtanen will pass by Earth a mere 7.2 million miles away. According to NASA’s Jet Propulsion Laboratory, this “will reach an estimated naked-eye magnitude of 3 to 7.5,” so it should be visible without binoculars or telescope, weather and light permitting.
46P/Wirtanen passes close to Earth every 5.4 years. Sunday's pass will be the 10th closest the comet has passed near Earth since 1950. The diameter of the comet is estimated to be 3/4 of a mile wide and moving at a speed of 21,000 miles per hour.
“Although the comet is moving relatively quickly through our solar system, it is still moving relatively slowly in our sky,” says Erin Hicks, Associate Professor of Astronomy and Director of the UAA Planetarium. “Its motion will be noticeable over the course of a few nights in that its position will shift with respect to the background stars. In a single night the comet’s location will appear to be unchanged and it will appear to simply move across the sky along with the stars.”
When the comet is closest to the earth on Sunday, it will be positioned “roughly between the constellation of Taurus and the Pleiades star cluster,” Hicks says.
Astronomy magazine Sky and Telescope says not to get your expectations too high. The comet is a dark object in the sky. The magazine says most people who view the comet will “typically describe it as a nearly circular cloud, comparable to or rivaling the Moon in angular size and appearing a bit brighter and more condensed near the center.”
As with viewing meteor showers and the aurora, the key to success on being able to see the 46P/Wirtanen comet is darkness. Get away from light pollution and find a completely dark sky. The moon is at its first quarter phase on Sunday, so will cast some additional light in the sky.
46P/Wirtanen was discovered on Jan. 17, 1948 by Carl Wirtanen at the Lick Observatory.