First measures of Visual Double Stars this year!

Thursday 20th August: A good clear night so instead of going to the Observatory, I set-up my own 8" SCT in the back garden. My first target of the night was Alpha Hercules, also known as Rasalgethi. This is a visual binary star which also happens to be a Variable. What is readily apparent when you observe this star is that when the star's variability is increased, then finding the secondary star can be tricky and sometimes cannot be seen at all. Normally though when the star in "quiet", the secondary can be easily seen and even measured see my website at http://www.abovethecloud.org.uk/ for my most recent measures. tonight, both stars were resolved as individuals but the Primary stars did look orange in colour, this is usually yellow wile the B-star appeared red.

Then I moved over to the lovely Globular Cluster, M13. Even in an 8" SCT, a very good and pleasing image can be seen. As this night is very clear with good transparency, M13 looks majestic. Plenty of stars were resolved in a misty ball.

After having a break due to cloud-cover, I got back to the scope at 2am BST to view Alpha Capricornus, a visual quadruple star-system! The system has a combined visual magnitude of 3.5. On closer inspection, using a telescope, the system is composed of two bright stars of equal magnitude, each having a fainter component that is easily resolvable in the scope with a 20mm lens.

It's now 02:30 BST and a target for measuring the position angle and separation of the stars; Gamma Delphinus in the constellation...Delphinus! Now I have already calibrated the configuration of 12mm reticule with the 45 degree prism and the 2.5x Barlow lens. So inserting the Barlow into the draw tube of the scope then the prism and the reticule gives a comfortable observing stance. When making measures, I can spend anything up to an hour to get one set of three measures in PA and Sep! Anyway, the bright primary star is yellow with the B-star being blue in colour. This is a fairly wide visual binary and easily resolvable even in small scopes. The arrangement of the stars is in an east-west configuration. My measure in PA (theta) is 269° and the separation (rho) is 10.8" which is +3° and +1.7" difference with the published values in the http://ad.usno.navy.mil/wds/ WDS, which I'm happy with as the WDS figures are averaged-out for the last complete year of measures, ie in this case 2008. See my web at http://www.abovethecloud.org.uk/ to see an image and the data.

One more before I hit the sack! 4am BST and I drop on the very wide visual binary, 61 Cygni. Both stars are of nearly equal magnitude and dark orange in colour. The configuration of the stars is in a north-west to south-east direction. Using the same configuration as above, I get theta as 150° and rho to 36.2" which is -1° and +5" difference to WDS. I'm reasonably happy with these but a recalibration will need to be done before the weather turns cold!

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