Friday, January 6, 2012

Winter deep sky objects

Last month some windows opened in the cloudy and rainy local weather that is the norm for December, which I put to good use to visit familiar and novel deep sky objects that are visible in the winter sky. Although I prefer to go to sites away from lights and passing vehicles, I frequently observe deep sky objects from my home despite the severe light pollution. Sometimes they show up surprisingly well through my 10 and 15-inch telescopes, sometimes I have to drive to a very dark area just to glimpse them through the 15-inch telescope. In any case there is always things to see regardless of where you're observing. Although I went to the airstrip to observe and sketch most of these objects, some were also observed and sketched at home.
NGC-1275 is the brightest member of a galaxy cluster in the constellation Perseus the hero some 300 million light years away from us. The other nearby galaxies NGC-1272, 1273 and 1276 are also members of this large galaxy cluster, most of whose members are elliptical and lenticular galaxies. All four of these objects are large elliptical galaxies devoid of massive blue stars. NGC-1275 is also a very strong radio source known as Perseus A, due to the presence of a super massive black hole in it's center feeding on gas, dust and stars that stray too close to it to escape. Visually it's merely an oval fuzzy object with a very bright inner core at 181X, which is billions of stars surrounding the black hole. Photographs show there is matter being ejected into space from the black hole and the galaxy is fairly similar to the nearby radio galaxy Centaurus A, another elliptical galaxy that is finishing off the last remnants of a spiral galaxy it recently merged with. In the surrounding sky I saw glimpses of other galaxies right at the edge of visibility all around this quartet of galaxies, but the seeing was poor and I wasn't able to use higher magnifications to pull them out from the sky glow.
The galaxy NGC-1404 in the constellation Fornax the furnace is normally an egg shaped elliptical galaxy, but recently the Type 1A supernova SN2011iv has appeared in it's halo. At 12th magnitude it's plainly visible and will remain so for some time before this exploded white dwarf fades from view. Also in the field is NGC-1399, another elliptical galaxy, both of which are bright with bright centers at 181X. These galaxies and about 16 others bright galaxies nearby are members of the small Fornax galaxy cluster, which is 60 million light years away. It's not well placed from my region of the country and is impossible to see from northern Europe, Asia and Canada due to the far southern declination, but farther south it's a rich hunting ground for those interested in observing galaxies of all types. It it possible to see 9 or 10 galaxies at a time here with a wide field eyepiece and a dark sky.
Fornax's compliment of deep sky objects is not limited to galaxies, it also contains the large and bright planetary nebula NGC-1360. This object is easy even in small telescopes to find and responds well to nebula filters too. From the southern U.S and Europe it is high in the sky enough to observe even with some light pollution present. Through a 6-inch NGC-1360 is a somewhat lopsided oval and through the 15-inch the central star is apparent. Strangely enough at 111X through the larger telescope the nebula is patchy and brighter along the ends. If you have a good view to the southern sky this is a great planetary nebula to observe.

Beyond the Fornax galaxy cluster there are other galaxies for modest telescopes such as the elliptical galaxy NGC-1395 in the constellation Eridanus the river. This 11th magnitude galaxy is small and bright, with a brighter core like most medium and large elliptical galaxies. This object is well within reach of a 6-inch or smaller telescope .
NGC-1385 is also an 11th magnitude object that is larger and is therefore fainter due to the lower surface brightness. This galaxy is an irregular or peculiar Sc type spiral galaxy whose spiral structure has a striking asymmetrical shape. Through the 15-inch I did not discern the spiral arms but did see a weak central brightening where the nuclear bulge was, and a somewhat irregular outline which does correspond to photos. A clearer night and better seeing would have allowed for higher magnifications, which would have helped show more structure in this galaxy, which undoubtedly was disturbed by a passing galaxy or a recent merger with another, smaller galaxy.
NGC-1371 is another Fornax galaxy that is bright and thus observable in small telescopes. This spiral galaxy shines at magnitude 10.8 and has a bright nuclear bulge. Like the Milky War it also is a barred-spiral galaxy with a weak central bar and a large disk, most of which was not evident but the portion I did see was subtly mottled or patchy, the first signs of it's spiral arms. No doubt higher magnifications and darker skies would reveal more of this fine spiral galaxy.
The bright open cluster M-38 is one of three wondrous open clusters in the constellation Auriga the Charioteer, but in the same low power field of view lies the overshadowed open cluster NGC-1907. This star cluster is an interesting object in it's own right though higher power eyepieces. Through the 15-inch at 227X, it looked very much like a star poor version of M-38. There were hints of numerous faint stars in the center. Overall, while not the equal of any of Auriga's big three Messier open clusters, it's an attractive and compact object that stands up well to light pollution and hazy skies.
NGC-7293 or the Helix nebula is one of my favorite objects. This planetary nebula is visible to large and small telescopes alike, but paradoxically it is also very faint despite it's apparent magnitude of 6. The reason for that is it's half the size of the full moon and therefore individual portions of it are very dim, but with a good  narrowband or O-III filter this object is visible from all but the most light polluted sites. At 142X through the 15-inch hints of the helices were visible despite the light pollution at the site. When the filter was removed, the central star became very noticeable but the nebula virtually disappeared. When the O-III filter was replaces the central star became very dim and the nebula became very distinct through the eyepiece. The best views to be had of this large wreath shaped planetary nebula is from very dark sites, but if you can get to any location where the sky is reasonably dark, this object is quite easy to observe thanks to nebula filters. This planetary nebula is probably the closest one to Earth, with a distance of about 450 light years.
NGC-2186 is one of many open clusters in Orion, though not nearly as well known as the Orion or Horsehead nebulas. This ninth magnitude object is scattered but surprisingly prominent from my home, although the rich starfields along the Milky Way makes finding the boundary of this cluster difficult. It's much better appreciated from a darker site than the suburbs of a larger city.
NGC-2196 is another open cluster located in the constellation Orion, but twice as large in apparent size as NGC-2186. It's a faiurly rich clump of moderately right stars and stood out better than it's apparent magnitude of 8.5 suggested from a bright urban location. Definitely worth another look from a darker site.
The open cluster NGC-2215 in the constellation Monoceros the Unicorn was the final object visited from my house with the 15-inch before I took down the telescope for the night. The star fields here are not as dense as the ones surrounding NGC-2186 and NGC-2194, and that made picking out the star cluster easier. It's apprent size and magnitude are similar to NGC-2194's, but it much easier to see as a distinct object. The arrangement of the brighter stars to me suggested the outline of an octopus, the cluster seemed to occupy most of the field of view despite the fact it's acutally much smaller than the moon in apparent size. Again, this open cluster seems worthy of a closer look from a darker site when the moon is absent.

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