Goodness, gracious, great balls of stars!
During this month’s lunar dark time, I got the imaging gear out to work the sky again and attempt to capture some new pictures. Before going out, I spent some time going through my boxes of adapters, connecting rings and focal reducers. I managed to get a set together that now allows me to image targets with my Celestron 11″ SCT at shorter focal lengths than I used to get my image of the Dumbbell nebula. Shorter focal lengths give me a wider field of view and collect more light in the equivalent exposure times. That means I can go for bigger targets and get more detail during my imaging sessions.
I don’t have a permanent set-up yet. So, each time I go out I have to assemble the mount and top it off with the telescope, guider and imaging gear. Then, I have to get things aligned to the North Celestial Pole and make a pointing model for my GOTO system. Hopefully, once all those steps are completed, everything tracks and guides correctly. But like any situation with a bunch of different parts making up a complete system, any number of variables can go wacky.
In the wee hours of July 13th, I had everything ready to go. But my polar alignment was a bit off. So, I had to interrupt the imaging software a couple of times to get my target re-centered. All in all though, I think this image turned out pretty well.
This time, my target was a globular cluster designated M15. It lies about 30,000 light years distant toward the direction of the constellation Pegasus. Globular clusters are giant, tightly gravitationally bound groupings of ancient stars with ages ranging from 10- 12+ billion years old. That makes these stars twice the age of a star like our sun. Depending upon the globbie observed, we are seeing hundreds of thousands, a half a million or more stars.
I made twenty-one two minute sub-exposures. Six with the Luminance filter (all colors) and 5 each using Red, Green and Blue filters. Total image time was 42 minutes. By adding a .63 focal reducer, I changed my 11″ SCT to a focal length of 1764mm.
The Milky Way galaxy has about 200 known globular clusters. They are a common feature of galaxy systems. The Andromeda Galaxy has an estimated population of 1,000 of these globbies. The super-giant elliptical galaxy M87 may have numbers approaching 10,000!
A survey of Milky Way globular clusters made by Harlow Shapely helped pinpoint our solar system’s location relative to the galactic core. I will explain more about how he did it in a future post.
