Wednesday, May 1, 2013

The Cast of Characters!

A week ago I posted the time-lapse of the Omega Centauri globular cluster rising past the 2.1 Meter Telescope of Kitt Peak National Observatory.  I was amazed how well the cluster, as well as a pair of galaxies showed up so well with 15 second exposures, which are what each of the frames was exposed!  While Omega is visible to the naked eye (and spectacular even in binoculars), Centaurus A is strictly barely visible in binocs, and NGC 4945 was unknown to me till glimpsed in an early version of these clips.  The labelled frame from the time-lapse is shown here to jog your memory...
The other night (29 April) I went out to photograph the individual cast of characters with my Celestron 14" (C-14).  My friend Marilyn came along for company, since Melinda had to work that night.  We were out near Kitt Peak to leave the sky glow behind us.  Because these objects are very low near the horizon, no light pollution could be tolerated.  The trip was also a test of the new (for me) AP1200 mounting, which I've used for visual use a number of times, but have yet to use for photography.  The C-14 was used with a Hyperstar - a lens system that allows the telescope to be used at prime focus - in this case, a 660mm lens at F/1.9 to keep exposures very short.  I also used a 1.4X tel-extender so I was actually shooting at 925mm focal length, F.2.6.  After finally getting everything aligned, installed and collimated, I started exposing, starting first with Omega Centauri.  While doing so, I also had installed my 70-200 zoom to shoot a wide-field tracked image of the trio using Melinda's camera.  That exposure is shown here with north up.  It is a total of 3 shots, total of 9 minutes exposure.  All 3 non-stellar objects are neatly shown, but it still surprises me they were visible in 15 second exposures!  Granted, that was with a wide, fast (F/1.8) lens...
Omega Centauri is beautiful pretty no matter how you observe it.  I was thinking this shot was pretty good, with 630 seconds total exposure, but as I was stacking the 10 exposures, the new Astronomy Picture of the Day featuring Omega came up.  It was shot from South America with the cluster nearly overhead, not 10 degrees off the horizon like it appears here.  So of course, the linked image is even more spectacular, but I still enjoy the one I took with my own setup.  The cluster is about 16,000 light years away from us, much nearer than the galaxies seen in the above wide views.  The description from APOD says there are 10 million stars in the cluster - simply amazing!
Next object I imaged was NGC 4945, as it was culminating very near the meridian.  Since it only reaches 9 degrees off the horizon maximum, every little bit helps.  This galaxy is actually pretty close to us as galaxies go, only about 12 million light years away.  At 9th magnitude it is barely seen in binoculars, but would be a lot more observed in the Northern Hemisphere if it rose higher in the sky!  This stack has 9 minutes total exposure.  The Wiki link above describes that this galaxy is in a nearby cluster along with Centaurus A, explaining why they are pretty close in the sky.  It is also quite large, the length is nearly 2/3 the diameter of the moon!  It would be nice to be able to go deeper with more exposure, but likely isn't worth it as low as it is...  The small elliptical at the left edge is NGC 4976, about 3X further away than 4945.
Finally it was time for Centaurus A, a most unusual-looking galaxy.  Also known as NGC 5128, its other designation identifies it as a radio source.  It is the 5th brightest galaxy in the sky, just below naked-eye visibility, and looks strange because of its spherical overall shape, but with a dark obscuring lane.  This image is only 5 frames with 6.5 minutes total exposure.
 Overall, it was a fun night and the Ap1200 worked flawlessly.  All the above exposures were taken WITHOUT guiding to assure accurate tracking!  I just let the mount track on the objects, and even with a little breeze, round images almost always resulted.  The only exception were the 2 frames from Centaurus A that I had to discard, otherwise, I included all images exposed!  I got back home right about 1am - a long night, but invigorating since I got to observe with my own equipment, looking at objects on my own list - as opposed to the public observing I've been doing lately.  I figured that this was just about the first time I've been out imaging with my own equipment in over 2 years!  Perhaps some more this weekend!


John Dolby said...

Love the HyperStar shots! I use a HyperStar, too, but never thought of combining it with a teleconverter! Like you, I love the snapshot aspect of shooting with a fast lens. And like you, I don't like to bother with flatfields and guiding and image-processing "work." I recently did a Messier Marathon with the HyperStar using 1-minute or less exposures (10-second subs). It was a fun 8 hours of shooting. I got only 61 M-objects (late start and poor preparation). But stacking the subsets and rotating, cropping, and identifying them (too lazy to keep a log while shooting) took me nearly 150 hours. I don't think I'll ever do that again! A curious result of that experience, though, shooting with just the telescope and a DSLR, got me interested to go mobile again. For a couple of years now I've enjoyed shooting from my back yard in Tucson, using a computer and tethered camera controlled over the home network. But you can't beat a dark sky. And since I don't need the computer for a DSLR, I might want to make an occasional trip to some place like Empire Ranch again, like we did back in the 80's. Does anybody go there anymore?

Dean said...

Hi John- Yes, the 1.4X works well, the 2X is a dog - don't even try! So it gives just a little more reach, perhaps at the expense of a little more vignetting.
I like being mobile and in a black sky. Generally no power, so that means no laptop, which means runnign the camera with a card, and batteries, or through the AC power adaptor through the car battery driving the mount. Empire Ranch (currently Cienega Ranch) has fallen out of favor in favor of the TAAA's CAC site. A little too far out for me, I favor a spot on the Kitt Peak highway for a pristine sky 75 minutes from Midtown. E-mail me for details, or join me sometime. -Dean