Comet 2012 K5 (Linear)

Comets are engaging objects to observe, particularly as the come through the inner solar system nearer the Earth and Sun. They can be quite rewarding to the observer who, following them from night to night, will see subtle changes in brightness and shape along with the occasional outbursts and dramatic changes. I enjoy reading the blog of Carl Hergenrother, The Transient Sky, as he regularly observes comets as part of his professional and personal work as an astronomer. In December and again this month Carl wrote about comet 2012 K5 (Linear) noting that 2012 K5 "is a long-period comet discovered by the LINEAR near-Earth asteroid survey program on May 25, 2012. At the time the comet was around magnitude 17-18. Though it passed through perihelion on Nov. 28 at a distance of 1.14 AU, the comet reached its brightest last month as it rapidly approached Earth. Close approach occurred at the very end of December at a distance of 0.29 AU (27 million miles or 44 million km).  Recent visual observations place the comet around magnitude ~8.6 at the end of December. Since the comet is now moving away from the Earth and Sun this month, it should rapidly fade to magnitude ~11.4 by the end of the month. The comet is now an evening object as it moves from Auriga through Taurus into Eridanus."

Last night was the clearest night we have had in about a week at the observatory, and I took advantage of the moonless sky to take a look at this outbound comet while it is still bright enough to appreciate. Using the Minor Planet Ephemeris and Comet Service I generated coordinates for the comet and directed the telescope to the specified location. (Note that this comet is moving rather quickly to the southwest, at a rate of 11.38 arcseconds per minute last night, so it is important that if you plan to observe this comet that you generate ephemerides for very close to the time you will be observing.) Currently, the comet is in Taurus and during the time of my observation was approximately .326 AU from Earth, which is about 2.7 light minutes.  The comet was immediately visible in an 8mm eyepiece (122X) using my TEC 140mm refractor. Below is my sketch of the comet from approximately 0440 UT on the 5th of January.

I have a difficult time estimating the brightness of diffuse objects, yet I would suspect that the comet is somewhere between magnitude 10 and 10.5. The nucleus is somewhat condensed and the coma fades quickly. There did appear to be a brighter section of a tail stretching out to the northeast, as I tried to capture in the sketch. This "brighter" ray was best seen with averted vision, but was not a difficult feature to note.

While I enjoy the conveniences of using the internet to generate precise coordinates as well as a "go-to" mount, if you are the type that enjoys the hunt, there is a detailed .pdf finder chart here that shows the comets path through late January. Whichever method you prefer, I encourage you to observe this interloper while you can!