Eyes Full Of Stars

A couple of weeks ago, I managed to get out and attempt more imaging. This time, I used a scope and mount set-up that I obtained 4 years ago. My original intention was to make  it my main imaging rig. But, I had some mechanical details to get sorted out. By selling off old astronomy gear I don’t use any more, I financed improvements for the mount and got it in top shape.

In the past I imaged unguided. That means I get the mount as close to properly polar aligned as possible and just hope for the best. If you look at my image of the Andromeda Galaxy, (it opens a new window) you can see the result of a careful polar alignment. But, I was only able to do 2 minute subexposures. The general rule of thumb is that longer subexposures are better. The best amateur imagers routinely work with 20 minutes subs or longer. Having a permanent mount really helps, but for now, I have to be patient and get the best results I can working with a portable set-up.

Without good alignment or proper guiding, long exposures show trailing or oblong stars. My goal was to be able to get as close to round star images as possible while capturing longer subexposures.

So, in late May, I put together a system to take guided images. Guiding means you track a star and make tiny corrections to the mount’s position to keep the star centered. In the old days, people would manually guide their images. They would sit hunched over the eyepiece for hours at a time. Now the process is handled by software. I had a monochrome camera left over from a project I did with New Mexico State Parks a few years back. That plus an old 8×50 finder scope that I never use gave me the basics to cobble together a finder/guider scope.

My CCD camera has a built-in guider. But, when I want to capture color images of these deep sky objects, I use a set of filters to get data for my target in Luminance (all colors), Red, Green and Blue. The built-in guider’s view of a guide star is effected by the color filters to the point that it can lose the guide star and cause trouble during the capture process.

The finder/guider scope I made is completely separate. It tracks a guide star while riding atop the main tube. On my laptop, have one program operating the CCD camera and filters for image capture and another running the guide scope tracking my chosen guide star and making corrections as necessary.

With this improvement, I was able to make 5 minute guided subexposures with my 11″ Celestron Schmidt-Cassegrain telescope at an insanely close-up focal length of 2800mm! The greater the focal length, the more quickly any problem with alignment or guiding will show itself. Here is an hour’s worth of image data using 5 minute subexposures and 3 frames per filter.

(click on it for a larger image)

M27 is shorthand for the official designation Messier 27.  Charles Messier discovered it in 1764. It became the 27th object listed in his  catalog of fuzzy, hazy objects that could be confused for the appearance of a comet. But, unlike actual comets, these fuzzy, hazy patches remain fixed against the background of stars. Messier compiled his catalog to index the location of  nebulae and avoid false reports of comet discoveries.  Pierre Mechain and Johann Bode collaborated with Messier by submitting objects they found for the catalog.

M27 is an example of the kind of nebula we expect our star, the Sun, to become during its terminal phase of evolution. Once our star reaches its red giant phase about 5 billion years from now, it will undergo mass loss by puffing off  its outer layers into the space surrounding it. The process can be erratic and happen in more than one stage. Ultimately, the core of the star is revealed, a stellar remnant destined to become a white dwarf star. The core of the star emits abundant and energetic streams of ultraviolet radiation. The UV radiation slams in to the debris field left behind by the red giant mass loss phase ionizing it and causing it to appear as of a  glowing patch of light.

M27 is about 1,200 light years distant toward the direction of the constellation Vulpecula.

This entry was posted on Friday, June 4th, 2010 at 11:38 am and is filed under General, Stargazing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.