Thursday, April 25, 2013

A Windy, Starry Night!

While we've had an abundance of clear skies in the Tucson area, up atop Kitt Peak, we've lost a lot of nights recently to high winds.  While most telescopes are protected by domes, as it nears 40mph, domes and telescopes are at risk from wind damage and rules dictate the observatory closes down. 

The last couple Spring observing seasons I've worked part time on the mountain, I've been working on a time lapse of the great globular cluster Omega Centauri rising over the 2.1 meter telescope.  After a couple tries I'd all but given up on the project, but last month I obtained a new tracking platform, made by Vixen.  One of the tracking options is half-speed, which splits the image blur between the stars and ground objects.  The setup is shown at left - the platform and camera is mounted on a standard tripod and it tracks along the horizon.  So while helping out on an astro-photo workshop a couple weeks ago (a very windy night), I tried out the combination with an 85mm, fast Nikon lens.  It worked great, but I aimed incorrectly so planned to go up a couple nights later.  Finally on tax day, after the Nightly Observing Program had been cancelled for wind, I decided to brave the elements and 5-day-old moon to try again.

The result is shown here.  Fortunately with the practice session a couple days earlier I knew when and where the cluster would rise.  The wind, gusting to 45mph made critical focus difficult by buffeting me around while trying to manually twist the lens grip, then I spent too much time getting the framing perfect - ball mounts are tough to aim in the dark with a camera body short on flat or straight edges to use a bubble level on...  So I didn't quite get the cluster rising over the trees.  The bright moon and F/1.8 lens speed made 15 second exposures possible (taken every 20 seconds), which was about perfect to minimize movement between frames.  As a bonus, besides the cluster, which clears our southern horizon by only about 10 degrees, the bright galaxy Centaurus A (NGC 5128) is visible a few degrees above it.  In addition, in my previous attempts at capturing Omega, I've noticed another sizable galaxy to the west, NGC 4945.  I've never seen it in a telescope, only on these pictures, but it is big and bright enough to try it next time I'm out.  The objects are pointed out in the annotated picture here...
Oh yes, and the time lapse is shown here - uploaded to YouTube for your convenience.  Full screen and HD quality always helps if you have the bandwidth.  Enjoy!



Andrew Cooper said...

Nice! I am going to try that half speed tracking trick!

Mark Trueblood said...

Dean, this is terrific! I have been out on that catwalk many times, as I use the 2.1-m about
4-6 nights each semester to improve the orbits of NEOs. Very nice sequence -- makes a great


Craig L said...

Dean, that is awesome! And it was cool to have seen you when I was on the mirror lab tour as well.

-Craig (from Pgh)