Saturday, June 5, 2010

Hercules Globulars

It has been awhile since I last posted any of my night time observations.  Despite the lack of blogging about the night sky, the Lost Pleiad Observatory continues to keep a scope to the sky 3-4 nights per week.  Last night was an exceptional night with skies that were very transparent, and fairly steady.  On the mount was my TEC 140 APO, which provides razor sharp images with excellent contrast.  I opened the observatory at about 7:30 PM so that the scope could acclimate, and at 8:00, I pointed the scope toward Saturn.

Always the romantic, I invited (begged) Beth to come and take a look at Saturn and a few of its moons.  She sat down and and when I explained to her that the single moon just off the rings was Tethys, she says "it looks like there are two moons there..."  I look and think to myself "no way," but always the good husband, I know to trust her.  I consult my new iPod with Sky Voyager (an incredible scope-side tool from Carina Software) and sure enough, Enceladus is right where she is describing it.  I look again, and with averted vision, sort of see it.  This is very impressive as Enceladus is about 1/10 the size of Titan, and very faint.  It is often lost in the glare of the planet and is only observable when it is at its furthest from Saturn in its orbit.  Below is a graphic representation of Saturn at the time of her observation.

After claiming her bounty, Beth headed back indoors and I spent some time planning my observations for the evening.  As the night progressed, it grew quite dark and I decided to have a look at M 13, the great Hercules Cluster.  I have observed this object many times, but it never ceases to amaze me.  To the right is a sketch I completed of this cluster some time back.  It does not do justice to the view in the eyepiece.  This cluster is approximately 23,400 light years away and has a diameter of around 140 light years!  It contains in the neighborhood of a half-million stars, which is impressive as typical globular clusters contain from tens of thousands to a couple hundreds of thousands of stars.  From a dark sky location, this cluster is bright enough to be seen with the naked eye as a fuzzy star.

I decided to observe two other globular clusters in Hercules, and first up was NGC 6229.  This little cluster is fairly bright, with a hint of mottling although resolving individual stars proved challenging.  At 196x, the cluster displayed a distinct core and a grainy outer halo.  It is joined in the eyepiece with two bright stars to the west, and together these objects form a pleasing image.  This cluster is much further than M 13, residing 102,000 light years away.  Despite the distance, the cluster shines at magnitude 9.4 and spans 4.5 arc-seconds.  To the left is my sketch of NGC 6229, and to the right is an image (reversed E-W) of this cluster from the Digital Sky Survey (DSS).

Since I was having fun in Hercules, I decided to slew the scope over to M 92 (NGC 6341), another fine globular cluster.  If this cluster were not neighbors with M 13, it would likely be observed more frequently and considered a showpiece object.  It is very large and rich, and at 25,000 light years partially resolved in my 140mm scope.  The cluster is twice the apparent size of NGC 6229, at 11.2 arc-seconds.  The actual diameter of this globular is approximately 80 light years.  As I spent some time trying to sketch this cluster, I noticed that there is a distinct chain of stars on the clusters east side.  In addition, there is somewhat of a gap in the outer portion of the cluster, on its west side.  To the right, is my sketch of this object.

Having had enough fun sketching, I turned my attention to some other globulars in the constellations Serpens, and Ophiuchus.  I observed NGC 6535, a faint and ghostly cluster nestled in amongst many faint stars; NGC 6539, another faint globular reminiscent of a dwarf galaxy; and, NGC 6517, which was faint and not resolved.  As it was approaching 11:30 PM and the milky way was well above the horizon, I took aim at some of the other famous Messier globulars such as M 10, M 12, and M 14.  Each of these is impressive and the views in the TEC were nothing short of spectacular.  I'll sign off this post with images of these objects.  The left image is M 10 taken by the Hubble Space Telescope, the center image is M 12 also by Hubble, and the right image is M 14 taken from Kitt Peak National Observatory with the .9 meter scope.

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