Have You Ever Seen a Comet?

The night sky has many treasures in store for us. Most of these objects are very far away, and don’t appear to change much from year to year. Without precise measurements with telescopes, they seem to be stationary. Others, like the Moon and the planets, are close enough that their motion is obvious.

In addition to the Moon and the planets, comets show visible progress as they move across the sky. Comets are icy objects which orbit the Sun. Unlike planets, comets have elongated orbits which bring them close to the Sun, and then take them far away from the Sun. For example, Comet Halley comes closer to the Sun than the planet Mercury, and then travels out to the vicinity of Neptune and Pluto.

When a comet approaches the Sun, the ice begins to evaporate. The water vapor, combined with soil, moves away from the surface, and forms a visible tail. Energy from the sun can ionize (add or remove electrons from) the water vapor, and cause a second tail to develop.

This month, a comet has made a close (11.6 kilometer) approach to Earth and is now moving away from us. It is called 46P/ Wirtanen. It is high in the sky for observers in the Northern Hemisphere. This week, the Moon is brightening and coming closer to “46P” every night. This interferes with a good look at the comet. Beginning December 23, 2018, the sky will be dark before the Moon has a chance to rise. For the following two weeks, the Moon will not interfere. (As always, don’t miss an opportunity to see 46P, even when the Moon is out.)

181213 image1 cropped — I obtained this image of Comet Wirtanen using a remote rental telescope on December 13, 2018. This comet has a faint tail, which doesn’t appear in this image. (itelescope.net T14; Takahashi 106 mm refractor, 5-minute exposure)

Comet Wirtanen is not bright enough to be seen naked-eye (to my best knowledge). Many people are finding it with binoculars and small telescopes. I have had an excellent view with my 10” (254mm) reflecting telescope.

Here is a link to a finder chart.

https://www.skyandtelescope.com/astronomy-news/observing-news/comet-46p-wirtanen-and-moon/

I admit that finder charts can be difficult to use. In this instance, however, the bright star Capella is a very good reference point. An alternative to paper charts is the free version of the smartphone app “SkySafari”. Once it is installed, simply tap “Search”, then “Brightest Comets”, then “46P Wirtanen”, then “center”.

Here are more links about Comet Wirtanen:

https://earthsky.org/todays-image/photos-comet-46p-wirtanen-brightest-comet-2018

https://www.space.com/42756-comet-46p-wirtanen-original-rosetta-target.html

https://earthsky.org/space/46p-wirtanen-possibly-visible-to-eye-dec-2018

Keep looking up!

John