AstronomyPicture of the Day—20181218

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2018December 18

CometWirtanen Passes by the Earth

ImageCredit & Copyright: Ruslan Merzlyakov (RMS Photography)

Explanation:Today Comet Wirtanen passes by the Earth. The kilometer-sized dirty snowballorbits the Sun every 5.4 years, ranging as far out as Jupiter and as close inas the Earth. Today Comet 46P/Wirtanen passes within only 31 lunar distances tothe Earth, the closest approach in 70 years. If you know where to look(Taurus), you can see the comet through binoculars as an unusual blue smudge.Pictured a week ago, Comet Wirtanen was photographed in the sky beyond an oldabandoned church in Skagen, Denmark. The image composite also captures theastrophotographer. After today, the comet will begin to fade as it recedes fromthe Earth and the Sun.