Comet 46P/Wirtanen Approaches Earth
For some time now, astronomers have been eagerly awaiting the return of a periodic comet named 46P/Wirtanen. This comet traverses the solar system like a commuter train - shuttling between the orbits of Jupiter and Earth on a 5.4 year-long cycle. But this December’s return is a special one for star-gazers throughout the world.
Comet 46P/Wirtanen will appear larger and brighter this year. It might even become bright enough to see without binoculars at locations away from artificial lights, especially when the moon is out of the night sky.
When any comet reaches perihelion, its closest approach to the sun, it becomes the most active – growing a halo (or coma) around its “dirty snowball” core and sporting one (or two) tails composed of released gases and dropped particles. Comet Wirtanen’s perihelion is only 6% farther from the sun than Earth’s orbit. Most of the time, Earth is somewhere else when the comet passes perihelion. But this year, we’ll be even closer to the comet, only 11.5 million km from it, on December 16.
Comet 46P/Wirtanen is predicted to brighten until December 16, when its orbit will carry it closest to both Earth and the sun. It’s now bright enough to see without binoculars if you are under a dark sky away from artificial lights. It’s quite easy in binoculars, if you know where to look. Don’t try searching for the comet with a telescope – the patch of sky seen in the eyepiece is so small that you’ll likely miss the comet. But once you know where it is, use the telescope to look closely at it!
Look for a faint, green, fuzzy blob surrounding a bright point of light. Reports are that the halo around the comet is as wide as a full moon – that’s half a finger’s width held at arm’s length. If Comet 46P/Wirtanen grows a tail, the tail will extend east (to the left), away from the sun. You can begin to look for the comet as soon as the sky is dark. The comet will then climb to its highest point, halfway up the southern sky, at around 10:15 pm local time. Then it will set in the west at about 4:20 am local time.
The orbit of this comet is carrying it up through the plane of the solar system from below. On Saturday night, the comet will land four finger widths (or 4.5°) below the very easy-to-identify Pleiades star cluster. That’s the bright little cluster of bluish stars above the very bright orange star Aldebaran in Taurus. On Sunday, the night when comet 46P/Wirtanen should be at peak brightness, the comet will shift to the lower left of the Pleiades.