Saturday, October 31, 2015

Summer giving way to fall

The humid, hot and hazy weather is finally giving way to cooler and clearer weather, at least between storm systems. Fall is normally the driest part of the year in my area, but that was not the case this year with a series of intense downpours that flooded my area. Once things dried out and a period of clear weather arrived, I drove out to the dark site with the 15-inch and began observing both favorite objects and others of interest that I haven't seen before.
NGC-6791 is an ancient and faint open cluster in Lyra which I have observed before but rarely have seen due to it's large apparent size and the faintness of it's stars. At a visual magnitude of 9.5 and an apparent size of 16-arc-minutes, this object is much fainter than it's apparent magnitude suggests. From a very dark site I've seen it as a mass of faint to very faint stars, which number in the thousands through my 10-inch. From the light polluted sites I normally use, it appears as a faint mist peppered with faint stars. It's quite easy to locate by star-hopping because there's two stars nearby that point out it's location.
In Pisces there's hordes of galaxies, but most are challenging to see at all in smaller telescopes. This quartet of galaxies however is easier to see than most, the brightest member on paper being the largest galaxy NGC-7782 which shines at magnitude 12.4. It shows a weak central brightening and was about 2 to 2.5 arc-minutes in length. The other members are all smaller but have bright cores. That combined with their much smaller apparent sizes actually makes them easier to pick out from the sky glow, even faint little NGC-7781 was spotted immediately. NGC-7779, has an apparent magnitude of 12.6, while NGC-7778 and NGC-7781 shine at magnitudes 12.7 and 14.2 respectively. Their apparent sizes of 1.6, 1, and .9-arc give all three a higher surface brightness than NGC-7782. This is a nice quartet of galaxies for a medium to large aperture telescope, with a fifth galaxy that was seen but not sketched just outside of the field of view. NGC-7780 is similar to NGC-7782 in magnitude and appearance. It lies just to the north of NGC-7782.
Over in Aries is another quartet of galaxies, made up of NGC-877, 871, 876 and 870, almost like a galactic "double-double" galaxy. However, I missed NGC-870 which is the faintest and smallest of the four. NGC-877 is the brightest, with a magnitude of 11.8 and an apparent size of 2.3 arc-minutes. It shows a very elongated, lens like outline and a bright central region, consistent with a barred-spiral galaxy nearly face on. NGC-876 is a tiny elongated object at a nearly right angle to its larger neighbor, and shines feebly at magnitude of 13.8, but because of it's tiny apparent size of 2.1 X .4 arc-minutes, the inner core of this edge on galaxy was readily visible, NGC-871 looked considerably fainter than NGC-877, with a sharp drop off in brightness along one side. The tiny and round galaxy NGC-870 lies nearby but remained invisible to me. NGC-871 shines at magnitude 13.2 and has an apparent size of  1.2 arc-minutes in length. It's oriented almost due north-south, with the southern end pointing towards NGC-870. That galaxy shines at magnitude 15.5 and is nearly stellar with an apparent size of about six arc seconds. If your skies are very dark and you have a large telescope, the galaxies UGC-1761 and FGC-270 also lie in the field, but they are even fainter than NGC-870.
Like Pisces, Pegasus is a rich hunting ground for anyone interested in observing galaxies. One lesser known but reasonably bright galaxy is the spiral galaxy NGC-7137. This relatively low surface brightness object was not difficult to find with the 15-inch due to it's apparent magnitude 12.7 and a apparent size of 1.6-arc minutes. This is a peculiar galaxy that has a round shape and it punctuated by bright knots in photographs with a bright outer ring. From dark sites a very large telescope would show interesting details in this galaxy, but under the rather poor seeing that night I did not try higher magnifications. It did appear just a little lumpy however,
NGC-976 is another Aries galaxy I had wanted to check out, and finally got the skies to do that.
It's fairly bright at magnitude 12.4 and it's small apparent size of 1.6 arc-minutes gives it a fairly high surface brightness. NGC-976 showed a strong brightening towards the center and an oval outline, with hints of patchiness where it's spiral arms are. It's Hubble classification of Sb makes it a twin of the Andromeda Galaxy, which is consistent with the large central brightening. This galaxy was well worth the effort to locate.
 
In addition to the objects above, I spent time gazing at M-31 and it's companions, M-33 and the face on spiral galaxy M-74 in Pisces. I also examines the Pisces galaxy NGC-182, and looked at the Veil Nebula. Since then the sky conditions have remained poor for observing deep sky objects. With luck, soon I will be able to observe them at the Deep South Regional Stargaze and put more of them onto paper.