Saturday, March 25, 2017

Return of the comets

Recently a number of comets have either entered the inner Solar System for the first time from far beyond the Kuiper belt or made another periodic return observable from Earth. As of now, four of them are nicely observable in modest telescopes if you can catch them from a reasonably dark site on a moonless night. Others are also observable, but much more challenging to see because they are either very faint, or incredibly diffuse. That is why I was not able to see the comet 45P/Honda-Mrkos-Pajdusakova at all even with my 15-inch, but 41P/Tuttle-Giacobini-Kresak was fairly easy to see with a 10-inch from the same site on a considerably poorer night. That comet is at this time in Ursa Major. The long period comet C/2016VZ18 PANSTARRS was small and faint, but I had little trouble spotting it with the same telescope. Both of these objects are well placed right now for evening observation. Two more comets for early risers or night owls that should be apparent in large binoculars and small telescopes is C/2015 ER61 PANSTARRS and C/2015 V2 Johnson are visible before dawn in Sagittarius and Hercules. They are well worth a look.

March is also a great time to peruse the star clusters and nebulae that line the winter Milky Way under warmer weather and at a convenient hour. One of my favorite winter star clusters is the open cluster M-93 in Puppis. Obvious in binoculars under good skies, through a 10-inch Dob even from my driveway it's bright, fairly large and looks like a mostly eaten pizza with the crumbs. Most of the stars are white or off white, but two bright orange stars also are within the cluster's boundaries. Whether or not they are related to M-93 I do not know.
One comet that moved from Perseus to Camelopardalis is the long period comet C/2016VZ18PANSTARRS. At the time of this drawing, it was about a magnitude 12.5 object that has a brighter center and an elongated shape, much like a distant spiral galaxy. It was faint and was best seen with averted vision. It will remain well placed for observation through this month into the next.
 Another fine winter star cluster is the very large and sprawling open cluster M-47 and it's neighbor, the smaller and fainter open cluster NGC-2423 which is to the lower right of M-47 in this drawing. It's a magnificent sight through my 11X56mm binoculars and even more so through a small to medium aperture telescope at low power through a wide or ultra-wide angle eyepiece. The bluish white stars are widely scattered in chains and clumps, far more than I could have sketched. Also in the same field is NCG-2423, which is a nice open cluster in its own right at higher magnifications, but at low power it tends to blend into the star field around it.
The best and brightest of the comets now in the inner Solar System is 41P/Tuttle-Giacobini-Kresak, a Jupiter family comet with an orbital period of 5.4 years and an orbital inclination of 9 degrees. At perihelion, it's one astronomical unit from the Sun as we are, at aphelion it's 5.1 AU from the Sun, just inside Jupiter's orbit. At the time of this drawing, it was around 7th magnitude, but it was very diffuse with a brighter inner region. This comet is close to the Earth, in the half hour or so I was watching it, it's motion against the background stars was very obvious. The skies were not very good at the time I was observing it, and I was not able to find it with my 11X56mm binoculars. It will however remain observable for quite some time, but act now if you want to catch this comet when it's fairly bright. It's next return will take place in 2022.