Monday, July 1, 2013

Messier 5

Messier 5 is a globular cluster in Serpens Caput (the Serpent's Head). It is one of the brighter globulars and is visible to the naked eye from dark locations.

For for those of you who are only interested in seeing the picture, here it is. Boring details about the imaging session are below. :)

Messier 5; ST80 on Vixen SP; 10x120 at ISO-800
Last night had nearly ideal viewing conditions, and I like to take any opportunity that I can to do some imaging or viewing, even if it's only for a short time. Fortunately the mount was already set up from the solar imaging session earlier that day, so I decided to work on improving my alignment skills.

Messier 5 was a good target for testing since it is fairly bright and was located near the celestial equator. As I've stated before, I use an old Vixen Super Polaris mount that was probably manufactured in the mid-1980s. The mount's polar alignment scope has an outdated reticle with a circle in which one is supposed to center Polaris. The circle is intersected by another circle that is drawn 48' from the center of the reticle, which represents the North Celestial Pole.  The position of Polaris has changed significantly due to precession, so I've had to estimate where to place Polaris in relation to the markings on the reticle. Until last night my attempts have been anywhere from bad to not quite so bad.

I downloaded an app named Polar Finder for my Android phone. It features an iOptron reticle that makes it easy to pinpoint where Polaris should be in my Vixen finder scope. I estimated the location in the reticle, aligned the mount, and then took 23 two-minute exposures.

The results were pretty good! There was a little bit of drift, but the main problem was just periodic error, which I have no control over, anyway. The image below is a combination of all of the exposures made in Startrails. It illustrates how much the mount moved off target during the session.

23 images combined in Startrails, showing the effects of periodic error and misalignment.
The stars are streaked up and down due to periodic error. I expected to see something more like the oscillations captured during the 1998 QE2 imaging session, but apparently the alignment was very good. I think that the small "hook" to the right was due to vibration or wind affecting the mount. I'm looking forward to trying this again and taking long exposures on some galaxies and nebulae!

No comments:

Post a Comment