A small comet named 46P/Wirtanen is currently approaching Earth and is expected to reach peak proximity on December 16, when it will swing by at a distance of 11,586,350 kilometers (7,199,424 miles) – about one-thirteenth the distance between our planet and the Sun.
According to skywatching expert Joe Rao, this inter-orbital encounter will be the tenth closest since 1950. As one of more than 400 “Jupiter-family” comets, 46P/Wirtanen has a long elliptical orbit with an aphelia – the point farthest from the Sun – near Jupiter. As it treks toward its perihelion – yep, you guessed it, the closest point to the Sun – on its 5.4-year orbit, the comet also comes closer to Earth. And every so often, our planet’s orbit happens to sync up in a way that puts us particularly cozy to its perihelion path (see video below). Luckily, 2018 is one of those years.
Here’s what you need to know if you want to witness this event. In the beginning of December, 46P will be present in the sky at a declination near -20°, between the constellations Cetus and Eridanus. By its drive-by on the 16th, the comet will be midway between the Hyades and Pleiades star clusters.
“By New Year's Eve, it will have rocketed on a north-northeast trajectory to a declination of +56 degrees into the constellation Lynx,” Rao wrote for Space.com. “For most midnorthern latitude locations, it will become circumpolar on the day after Christmas; in other words, just as the Big Dipper or Cassiopeia appear for most northern locations, it will neither rise nor set, but rather be visible in the northern sky all night long.”