Homepage Backyard-astro

The Deepsky Lists Logs Deepsky reports Top-100 Binocular objects

4 May 2003: M92, M13, Alpha Herculis and Delta Herculis

Last night I paid a short visit to Hercules.

I used the TAL 200K with Vixen eyepieces. I started of with M92, a beautiful globular cluster in Hercules. To find it I centred the TELRAD at 44 eta Herculis. Then I switched to the finder scope. I started to move the telescope in a straight line from 44 eta to 85 iota Herculis. At almost two third of the distance between the two stars, I noted a fuzzy patch in my finder scope. This was M92. It switched to the eyepiece and tried a wide range of magnifications. At 133 times it looked stunning. In the periphery outside of the core it could be resolved into many stars, arranged in several chains, mainly in the northern and southern direction. This class IV globular cluster has a diameter of 11.2' and a visual magnitude of 6.4. It was discovered in December 1777 by J.E. Bode. Messier discovered it indepenent from Bode in March 1781. A beauty!

Next on the list was M13, the finest globular cluster for observers on the Northern Hemisphere. It is very easy to locate. Again I centered the TELRAD on 44 eta Hercules. I switched to the viewfinder and started to move in the direction of 40 zeta Hercules. I noticed a large fuzzy patch immediately. Once I had it centered and again I switched to the eyepiece. Wow, even under light polluted skies M13 is beautiful. No matter what magnification I used, there were always interesting things to see. I used all my eyepieces (magnifications 62, 80, 100, 133, 166, 200, 222, 286). It even looked better using averted vision. The favourite magnification for this one is hard to choose. At 60 times M13 lies beautiful in it's surroundings, at 133 or 166 times it can be resolved almost into the core, and at 286 times you get the idea that you have resolved it, and due to the darker sky, you see much more stars around the core. There are many streams of stars into almost all directions, all originating from the core. I hope that one day I can see this cluster under better conditions. This is my favourite!

Next I went to visit 65 delta Herculis, a very nice double. It is very easy to locate, halfway between epsilon and alpha Herculis. It is an optical double. The a component, a white star of magnitude 3.1 has no real connection with it's optical companion of magnitude 8.2. The separation is 9" and the position angle is 236 degees. F.G.W. Struve measured the separation in 1830. It was 25.8". In 1960 it was about 9" at a position angle of 241 degrees. I could not detect any colour in the both the A and B component. They looked white to me.

Then I went to my last target for this night, 64 alpha Herculis, again a double star. This is the fifth brightest star of Hercules, and very easy to detect. I just used the TELRAD again to centre it. Alpha Herculis is also known as Ras Algheti or Struve 2140. According to Burnham, the name Ras Algheti is derived from Al Jathiyy, the Head of the Kneeler. The kneeler is Heracles (Greek) or Hercules (Roman). Alpha Herculis A is a variable and is some 410 light years away from us. The A and B component have a separation of 4.7". The position angle is 107 degrees. A is of magnitude 3.5 and B is of magnitude 5.4. A was definitely orange. In B I could not detect any colour. To me it looked white. This is a beautiful pair for every telescope! At 23.00 UT it started to get cloudy, but still I was very pleased with the four objects I had seen. Whatever telescope you use, they should be on your observing list.


Hercules Finder Chart made with TheSky for Macintosh

Sketch Herculis 64

64 alpha Herculis

Sketch Herculis 65

65 alpha Herculis

Copyright © 2003 www.backyard-astro.com