Looking through photos taken in the past few days by NASA’s Solar Terrestrial Relations Observatory (STEREO) Comet ISON appears to be chasing Comet 2P/Encke as it dives toward the sun. You can watch their day-to-day progress by clicking HERE and selecting “HI Stars A” from the menu on the left side of your screen. Next, click on “1024 resolution” and then on a date link to see the image. It’s very cool to watch the comets’ changing positions even over the course of a day.
Today ISON and Encke are stacked one atop the other. That’s line of sight only of course, since they’re actually separated by millions of miles. Encke passed perihelion, its closest point to the sun, on Nov. 21 at a distance of 30.7 million miles; ISON misses the sun by only 730,000 miles this Thursday.
Encke is an interesting comet in its own right. Discovered in 1786 by French astronomer Pierre Mechain, it was found in1819 to be a periodic or returning comet. Johann Encke first computed its orbit, which at 3.3 years, is the shortest verified orbital period known for a comet.
During the current swing-by, Encke showed up in the morning sky in August and remained visible through early November. The comet will be too near the sun to observe for the next few months as it fades from view. Farewell for another 3.3 years!
Keep a close eye on ISON. Word comes that production of certain molecules within the comet has dropped dramatically, which some astronomers are interpret as a sign that the icy core or nucleus of the comet is breaking up. Everything appears intact in the photos, but their resolution is not enough to reveal a breakup until large fragments begin streaming down the tail. We’ll have to wait and see.
I’ve written a guide for viewing Comet ISON on perihelion day when it will be brightest for the online publication Universe Today. Check it out if you like, otherwise I’ll provide an updated, condensed version here on the blog Wednesday.