Monday, February 22, 2016

Another bounty of winter objects and a comet

So far the winter weather has been cloudy, rainy and windy with few good opportunities to observe deep sky objects without the moon lighting up the sky. To make things even more challenging, the seeing has been horrid, so bad that even at low power everything boils like it's at the bottom of a water filled pot boiling on the stove. So when the chance to observe a few objects under skies darker than I have at home came last weekend, I seized it. I packed up the 10-inch, and my new 30mm Explore Scientific 82 degree wide field eyepiece and drove to a darker site north of my city. Once I set up, I quickly got to work on a short list of objects I was interested in.
Comet C/2013US2010 finally became observable without me having to roll out of the bed at 4:00 a.m. to see it a month before, but poor weather and other considerations prevented a good look at it until last weekend. At 149X the coma and nucleus were bright and resembled an E0 elliptical galaxy with the appearance of having two tails widely separated. The ion tail is longer and narrower while the dust tail was wider, fainter and shorter with a wedge shape. Overall the comet was between eight and ninth magnitude and will remain visible to amateur telescopes for quite some time to come.

One object I long had an interest in was the supernova remnant IC-443, also known as the Jellyfish Nebula. However, this nebula proved to be anything but easy to see. Finally a period of good sky transparency and an Orion O-III filters on my 18mm Explore Scientific 82 degree eyepiece revealed an elongated, patchy and very dim object that was shaped somewhat like the bell of a jellyfish without the tentacles. I was quite surprised to see it with my 10-inch from a site with heavy light pollution along the southern horizon, but there it was at 73X. I'm definitely am going to have to come back to this nebula at a darker site with my 15-inch to see what if any additional structure would be visible. IC-443 is merely the brightest region of a quite asymmetrical supernova remnant created between 1,000 and 30,000 years ago. Long exposure photos of the region show other, much dimmer patches of nebulosity in the area rather like the Veil Nebula.
Clouds however moved in and forced me to pack up and go home after observing IC-443, so I resumed observing objects at home the next clear night. I spend the evening looking at the usual favorites that are visible from home plus three open clusters in Gemini I never seen before or observed in the past but did not sketch them. NGC-2331 was spotted the week before during the local club's star party but I did not get the chance to sketch it then. As such it is a fairly bright, large and scattered open cluster that seems to form the outline of a boot or a sled. It was surprisingly visible through the light pollution I have to live with at home. Shining at ninth magnitude and spanning 18-arc-minutes of sky, this open cluster has a curious circlet of six stars on the eastern side. It should be fairly obvious though modest telescopes under good skies. In all, NGC-2331 shows about 40 stars through larger telescopes.

NGC-2355 is somewhat smaller and richer, with it's stars closer together.
Shining at 10th magnitude, it's 50 stars are spread out across nine arc-minutes of sky. From my driveway, it was easier to tell apart from the surrounding stars than NGC-2331. It resembles a cherry or a bomb with a lit fuse, the end of which is marked by a bright field star. NGC-2355 is a fairly rich open cluster that has stars that seem to be arranged in lanes. It is definitely a good object for modest telescope where skies are reasonably dark.

NGC-2395 is yet another of many open clusters scattered across the star fields of Gemini.
This eighth magnitude open cluster's 50 stars shine at 10th magnitude and fainter, arranged in  a pattern that vaguely resembles a bat in flight. Half a degree away lies the unusual and lopsided planetary nebula Abell 21, also known as the Medusa Nebula. This star cluster is not a rich one, it's stars are quite scattered across 12 arc-minutes of sky.

Sharpless2-308, also known as RCW-11 is a huge but faint nebula in the southern reaches of Canis Major, the big hunting dog. Despite its resemblance to the Veil Nebula in photographs, it is not a supernova remnant. In fact it's the outer layers of the Wolf-Rayet stat EZ Canis Majoris ejected into interstellar space as a Wolf-Rayet shell. Like the very similar Crescent Nebula in Cygnus, it's made up of faster stellar winds catching up with and overtaking slower moving material ejected earlier in the star's history, Through my 10-inch fitted with a 30mm Explore Scientific 82 degree eyepiece and an Orion O-III filter, the nebula was quickly located once the star that created it was located. It was a nearly round bubble like object with a pronounced brightening on one side, fading to near invisibility on the other at 44X. That eyepiece when used with the 10-inch and a Paracorr yields a true field of view almost 1.9 degrees across, with Sh2-308 spanning nearly a degree of sky. It's low elevation surprisingly enough was not a problem when I was observing it. In a few hundred thousand years or less, EZ Canis Majoris will explode as a Type 1b or 1c supernova, and destroy this shell when the fast moving debris from the blast reaches it. This is a quite spectacular object that can be seen in telescopes as small as 80mm in aperture under good skies.