A COMET AS BIG AS THE FULL MOON: On Dec. 12th, Comet 46P/Wirtanen will approach Earth less than 1.5 million km away–making it one of the 10 closest-approaching comets of the Space Age.
It’s a small comet, with a nucleus barely 1 km wide, but such proximity makes even small things appear large.
The comet’s gaseous atmosphere is now as wide as a full Moon. Mike Broussard of Perry, Louisiana, photographed the comet on Dec. 2nd and inserted the Moon for scale:
“The comet still has a couple of weeks before closest approach and it is already as big as a full Moon,” says Broussard, who could see the comet with his naked eye–“just barely using averted vision and only when it was in the darkest section of the sky,” he adds.
Wirtanen’s relatively small core of dirty ice cannot produce enough gas and dust to create a really bright, flamboyant tail. The best case scenario is probably a big diffuse cloud of magnitude +3 or +4, barely visible to the unaided eye but an easy target for binoculars and small wide-field telescopes.
Diagram from “Why is Wirtanen’s 2018 Apparition Historic?“
On the nights of closest approach, 46P/Wirtanen can be found in the constellation Taurus rising in the east at sunset and high in the sky at midnight. Explore these links for more information: sky map; ephemeris; 3D orbit; light curve.
Pictures of 46P/Wirtanen (2018)