Wednesday, June 26, 2013

Spring NGC galaxies

Amazingly, a clear and cool night came that offered good skies and moderate for my area, dewing. I loaded the 15-inch into the car and headed out to a darker site than the driveway in search of galaxies not observable from home. I quickly found the sky conditions made the hour long trip worth while. The mosquitoes were out in force, fortunately I remembered to bring the bug repellent. First on the list was the Whirlpool Galaxy, also known as M-51. The spiral arms were clearly apparent, and so was the structure of the companion, NGC-5195. Not only was a brighter core evident, so was the "bridge" that appears to link it to M-51 as well as the comma like shape. Both were an impressive sight at 227X, and the distortion of the larger galaxy by it's interaction with NGC-5195 was also evident. M-51 is one of my most favorite galaxies, and one of the most impressive in the northern skies.
Two objects of interest I had wanted to look over in Hydra were the elliptical galaxies NGC-3904 and NGC-3923. NGC-3904 was fairly bright with an obvious central core, and like most elliptical galaxies it has an oval shape. From a good site it's fairly easy to see, it definitely does not require a 15-inch to bring it into view. Aside from the brightening towards the center little if any structure was apparent at 227X. Shining at 11th magnitude, NGC-3904 has a small apparent size of 1.9 X 2.7 arc-minutes.
Nearby also lies another elliptical galaxy in Hydra, NGC-3923. This galaxy is larger in apparent size and brighter at an apparent magnitude of 10.1. I've managed to spot it from my driveway with the 15-inch when sky conditions were very favorable. Like NGC-3904, this galaxy has an oval shape but a weaker brightening towards the center. A quite easy object from a good site, it definitely is a galaxy small telescopes can reveal to backyard astronomers.
One class of objects that always intrigued me are trios, quartets and even larger assemblages of galaxies visible in one view through a telescope. Hickson 61 is one such object I have observed before with my 10-inch, but I was then only able to see the bright elliptical and lenticular galaxies. This time the fourth galaxy appeared when I brought the 15-inch to bear on it and ran the magnification up to 300X. It was very faint and was only seen with averted vision. Interestingly, it is not associated with the other three, it is in fact a foreground system far closer to us. The galaxies of Hickson 61 are NGC-4169, NGC-4173, NGC-4174 and NGC-4175, with NGC-4173 being the faintest. NGC-4173 is a flat Scd galaxy with a magnitude of 12.7 and an apparent size of .7 X  5 arc-minutes. It appears as a ghostly streak pointed in the same direction as one of it's brighter neighbors. NGC-4169 is a magnitude 12.3,  SO lenticular galaxy with an apparent size of 1.8 X .9 arc-minutes but it looks smaller than that through the eyepiece. It has a very bright inner core. NGC-4174 and NGC-4175 shine at magnitude 13.5 and 13.4. Their small apparent sizes give them fairly high surface brightnesses, enough to make spotting them through modest telescopes not too difficult even from less than very dark skies. With the exception of NGC-4173, the other three galaxies are members of a galaxy group whose brightest member is NGC-4169. This quartet is a captivating find for those who enjoy observing galaxies and galaxy groups.
Virgo holds many fine galaxies for amateur telescopes, so many in fact it's difficult to give all of them the observation they deserve. Two such galaxies are the elliptical system NGC-4261 and the barred spiral or possibly lenticular system NGC-4264. NGC-4261 is very bright, so bright I was able to see it with ease through the 15-inch at home. NGC-4264 required a drive outside of Mobile to be seen with the same telescope. Both made a fine pair from a reasonably dark site, and they certainly would be accessible to a 6 or 8-inch telescope.
NGC-4570 is a flattened, nearly edge-on lenticular system also in Virgo that is overshadowed by the Messier and better known NGC galaxies there. It is however a quite interesting galaxy in its own right, with a long spindle like outline and an elongated bright inner core. Quite small, it withstands high magnifications through larger telescopes. NGC-4570 has a magnitude of 10.9 and a high surface brightness of 12.4 due to it's small apparent size of 1.1 by 3.8 arc-minutes.
NGC-4596 is another lenticular or a transitional lenticular-barred spiral galaxy in Virgo. Very bright at magnitude 10.5, I noticed the inner region was elongate but did not see the bar that is apparent in photos. Surrounding the inner core was a faint, oval hazy halo. Although it's brighter than NGC-4570, it appears dimmer through the eyepiece due to it's considerably lower surface brightness of 13.3 and larger apparent size of 3 by 4 arc-minutes. This galaxy probably would reward users of large telescopes from dark skies seeking to see evidence of it's barred spiral structure, but my observing site is not quite dark enough for that.
Yet another bright elliptical galaxy in Virgo is NGC-4636. Shining at magnitude 9.7, this galaxy shows a very rapid brightening towards the center and an egg shaped outline. Otherwise in appearance NGC-4636 resembles an unresolved globular cluster. Much larger than the previous Virgo galaxies in apparent size, NGC-4636 has a surface brightness of 13.3 and an apparent size of 6 X 4.7 arc-minutes. This is an easy object for a modest telescope from a good site.
Bootes does not have the rich assortment of galaxies within reach of amateur telescopes that Virgo does, but it does have some galactic treasures of its own. One such treasure is the galaxy trio NGC-5529, PGC 50952 and PGC 50925. The NGC galaxy is an flat Sc spiral galaxy nearly edge on with a magnitude of 12.2. It is quite faint and difficult for smaller telescopes unless the skies are very dark. From the light polluted site I found it from, it was a very dim slash with a elongated, weak central brightening. The two PGC galaxies, both of which are nearly 15th magnitude objects were only visible through averted vision as very faint, featureless oval blobs, with a slight if any central brightening. I had to jiggle the telescope to be sure I was actually seeing them and not random noise in my vision. NGC-5529 has a surface brightness of 13.8 and an apparent size of 6.2 X .8 arc-minutes. Despite its listed apparent magnitude, under the conditions I was observing this trio NGC-5529 appeared to have a magnitude closer to 13 to me. No sign of the dust lane appeared, nor did I see the warping in the disk. Both probably would appear from a darker site in a future trip to a star party.
Much brighter in appearance is the Bootes galaxy NGC-5689, a SB-0 barred spiral galaxy nearly edge on. Shining at magnitude 11.9, it has a fairly high surface brightness due to it's apparent size of 1 X 3.5 arc minutes. It sharply brightens towards the center, and is the brightest member of a small group of galaxies. The core appears elongated or seems to have wings, where the central bar is located.
The final galaxy I drew was diminutive NGC-5820 in Bootes. Very small it required 298X for the best view, which fortunately the seeing allowed that night. This lenticular galaxy has a magnitude of 11.7 and a high surface brightness of 12.2 due to it very small apparent size of 1.7 X 1.1 arc-minutes. Unlike many galaxies, NGC-5820 responds very well to high magnification. Nearby is another much dimmer galaxy, NGC-5821 which I did not notice that night. Very faint and small, it's apparent magnitude of 13.8 and being directly behind a foreground star in the Milky Way makes it a tough proposition from the usual skies I observe from. I plan to return to this pair at a very dark site to sketch the field again. NGC-5821 itself is a spiral galaxy that is difficult even in large telescopes, unlike it's far brighter neighbor.
This night was a most rewarding foray deep into the wider Universe. While observing and sketching these objects, I stopped by some other galaxies and star clusters too. NGC-5248, the brightest galaxy in Bootes showed signs of it's spiral structure, and the globular cluster NGC-5466 also in Bootes resembles a swarm of fire flies in the darkness at 227X. I also looked at the Lagoon, Trifid and Swan nebulae in Sagittarius, all of which showed magnificent views of their structure. M-4 displayed it's central bar even at low power, with stars showing hints of their actual colors at 227X. Nearby M-80 showed itself as a tiny pinch of sand, and the dim little globular cluster NGC-6144 near Antares also partially resolved into very faint stars. In smaller telescopes from my area, it appears merely as a faint blur. The Scorpius globular M-62 showed it's lopsided nature and nearby NGC-6441 also resolved into stars around the outer edges at 298X. In Sagittarius, the open cluster NGC-6520 and it's associated dark nebula B-86 looked as though someone cut out a piece of the sky and dropped it. B-86 looked like the dark cloud of gas and dust it is, it's very apparent at 227X. M-22 also showed thousands of star, some of which glowed with a reddish orange color. It was a memorable night under the stars, one an amateur astronomer can never see too many of.