Thursday, March 1, 2012

A break in the doldrums

During the past month, clouds, rain and wind have left few opportunities to observe, so when a golden opportunity arrived last week, I made use of it to explore the numerous winter open star clusters  visible from my home. Along the winter Milky Way scores of open star clusters exist ranging from huge binoculars only objects down to small faint patches of light that require a large telescope to make out. In places they overlap one another or are connected with emission and or reflection nebulosity. All are in range of a small telescope from darker sites, but I was using my 15-inch at my light polluted driveway to make these drawings. Because I live at latitude 30 degree and 42 minutes North, these objects get high enough in the sky, but for people who live in Canada, Russia and Northern Europe many of these star clusters are going to be a lot harder to see because they will be very near the southern horizon, requiring a darker and clearer night that I would to find them. Low and medium power eyepieces are best for these star clusters, you can see many of them very well at 100X.
NGC-2367 is an open cluster in eastern Canis Major, the large hunting dog, near the double star h3945, also known as the "Winter Albireo" due to it resembling the famous and bright double star, Beta Cygni. This cluster seems to consist of two concentrations of stars, but the central core is a bright Y formation of stars. Fairly small and shining at 8th magnitude, it's fairly inconspicuous among the dense star fields of Canis Major.
NGC-2384 is smaller than NGC-2367 in apparent size, but easier to distinguish from the surrounding star fields thanks to it being an elongated group of stars flanked by two bright double stars. There is also a formation of stars that resembled a golf club or a letter L. Brighter than NGC-2367, NGC-2384 is also flanked by the neighboring open cluster NGC-2383, which I was not quite able to tell apart from the surrounding stars. I plan to return to this object to see if I can get a better look at it.
NGC-2421 is an open cluster about four degrees due east of NGC-2384 in the constellation Puppis. Much larger in apparent size than the two Canis Major objects, it's easier to tell apart from the surrounding star clouds despite it's stars being dimmer. The stars are arranged in a somewhat triangular grouping some 10 arc-minutes across, or a third of the diameter of the full moon. This is a rich and nice open cluster among the many that lie in Puppis and better placed for observation from the northern hemisphere than most of Puppis' deep sky objects.
NGC-2479 is yet another of Puppis' open clusters, which would get more attention from amateurs had the bright Messier open clusters M-46 and M-47 weren't a mere five degrees or so to it's northwest. Quite small and compact, it reminded me of a broken wedding ring, with the brightest star being the diamond. The broken wedding ring appearance persists in photos of this 10th magnitude object. It was surprisingly visible from my home given the heavy light pollution present.
NGC-2482 is a large, rich and bright open cluster, with a elongated shape and near a triangle of bright field stars. It's some three degrees east-southeast of the bright Messier open cluster M-93 and compares favorably to it in brightness, stellar population and standing out well from the surrounding star field. From a dark site it would be visible in larger binoculars and is a fine sight for a 6-inch telescope.
NGC-2509 is yet another open cluster in Puppis, a rich and much brighter than it's apparent magnitude of 9 suggests. It's quite small and responds to magnification well even though it's apparent size is about one quarter that of the full moon. While there are several dozen bright stars visible, it seems there's a background of very dim stars, shimmering like star dust among them. It almost gave the star cluster the appearance of being shaped like the letter Y. This object is a good one for smaller telescopes, it's dense and rich stellar population makes locating it easy from a good site.
NGC-2539 lies about ten degrees to the east-northeast of the bright open cluster M-46 in the northeastern corner of Puppis. A large, rich open cluster, NGC-2539 spans some 22 arc-minutes of sky and shines at magnitude 6.5, making this an easy object for binoculars and small telescopes. At142X, it took up most of the field of view with it's hundreds of stars, though I was only able to see the brighter members from my home. Doubtlessly this cluster would be a very spectacular object even with a small telescope from a dark site. The star cluster is flanked by a convenient bright star which marks its position for easy star hopping, itself a nice double star in it's own right.
While Puppis is host to three Messier and numerous NGC and IC objects, it also is home for a number of other deep sky objects discovered and cataloged after these catalogs were published. Trumpler 7 is one such object, and open cluster discovered by the American astronomer Robert Trumpler in the 1930's. Altogether Trumpler cataloged some 330 open clusters, most of which were previously unknown to astronomers. Trumpler 7 is also listed as CollinderCanis Major and Puppis, two degrees to the east-northeast of the star Tau Canis Majoris, which is surrounded by the magnificent and brilliant open star cluster, NGC-2362.
Abell 12. Ordinarily, a planetary nebula of it's apparent size and brightness would be an easy object for small telescopes, but Abell 12 is nearly hidden in the glare of the fourth magnitude star Mu Orionis. As such, it's a very difficult and maddening object to find. However nebula filters help make searching for it easier, and steady seeing is important for success in finding this planetary nebula that hides in plain sight. Were it not nearly hidden from views, it would certainly be listed in the New General or Index Catalog. This object was finally revealed through the use of a 4.7mm eyepiece that yielded 280X, drawing the nebula far away enough from the star to make it visible as a dim oval nearly lost in the glare.
Other objects I have been observing include some less well known open clusters in Cassiopeia and Perseus, which will soon be lost in the twilight, then will re-appear in the early morning skies. One such object is the huge open cluster, Stock 2. This open cluster like many cataloged by the American astronomer James Stock was missed by earlier surveys of the sky before he discovered it.  This cluster is very large, at least a degree across and therefore really is best for small telescopes with low-power, wide field eyepieces and binoculars. In appearance it resembles an X of seventh through ninth magnitude stars. Some observers call it the "Muscleman Cluster because of it's resemblance to a headless weight lifter. It's easy to find only two degrees north of the Double Cluster and the whole object shines at fourth magnitude.
Stock 23 is not as rich as Stock 2, but it is situated in a rich Milky Way field with other stars scattered across the area. It was easier to see than I expected from the driveway, which combined with it's large apparent size of one degree and total magnitude of 4.4 makes Stock 2 an ideal object for binoculars and small, lower power telescopes.
Smaller than Stock 23, the large and scattered open cluster Trumpler 3 has a curious kite like shape. Shining at seventh magnitude ans some 23 arc-minutes across, the brighter stars readily distinguish it from the Milky Way's star clouds in Cassiopeia. An excellent object for small telescopes, Trumpler 3 lies near the border with the large and faint constellation, Cameleopardalis, the Giraffe.
One of my favorite objects in the entire sky is NGC-3242, also known as the "Ghost of Jupiter," in the constellation Hydra. This planetary nebula is extremely bright and shows up easily though any telescope. The larger and more powerful the telescope and the greater the magnification, the more detail you will see. This time I trained the 15-inch on the nebula, which showed the central star clearly in the center of the nebula surrounded by the eye like inner shell. Around that lies the outer shell, whose ends along the long axis of it's oval shape were much fainter than the rest of it. The whole nebula has a very strong blue-green or turquoise color. At 300X or above through a medium or large aperture telescope, NGC-3242 is a magnificent  deep sky object even from a city.
Last but not least, I observed the nearby white Main Sequence star Sirius, the brightest star in the sky in an effort to locate it's companion, the white dwarf Sirius B. This dead star packs the mass of the Sun into a sphere smaller than the Earth, resulting in a crushing surface gravity 900,000 times greater than at sea level on Earth. The star is very faint, and shines 10,000 times dimmer than the bright star. Despite it's feeble luminosity, the surface is a searing 25,000 degrees Celsius, much hotter than Sirius A whose surface is at 10,000 degrees Celsius. That gives the white dwarf a bluish cast, but it's usually hidden in the glare of Sirius A unless the star is near the far end of it's orbit and the seeing steady. Until 2022, it's going to move farther and farther away from Sirius A making it easier to spot. At present it is some ten arc-seconds due east of the primary star, visible as a tiny blue white pip of light that follows Sirus A as both drift across the field of view. I was seeing it come and go due to turbulence in the atmosphere above me. I have tried many times to see this stellar corpse, but only see it very few times with my 10-inch or larger telescopes. Curiously, while I was able to see the white dwarf through my ES 4.7mm 82 degree eyepiece, it was not visible through a more powerful 3.5mm Orion Stratus. Clearly, the optics and coatings of the ES eyepiece were better than the Orion Stratus, enough to make the difference between seeing Sirius B and missing it. I'm looking forwards to warmer and drier weather so I can begin to observe the galaxies of spring, and re-acquire comet Garrad, which is now about to make it's closest approach to Earth on the way out into deep space.


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