Sunday, August 11, 2013

Pipe or Horsie?

I spent a few hours on Kitt Peak the other night and posted the Iridium Flare shot that was my first exposure of the night.  The next couple hours was spent on a 3-panel mosaic near the center of the Milky Way Galaxy - one of my favorite fields, the Prancing Horse Nebula.  Shown here is a wide field shot from a couple years ago from an observing session with our friend Christian.  Regulars know I'm a fan of dark nebulae - clouds of dust and gas silhouetted against distant cloud of stars behind it.  The left side of the frame shows the network of dark clouds known as either the "Pipe Nebula" or the "Prancing Horse Nebula".  You've got to use your imagination, but both can be made out.


One way to improve an image is to expose longer, another way is to use a telephoto lens and assemble a mosaic of the field.  This has the advantage of improving the resolution of the target object.  Using the (relatively new) Polarie tracking platform, I shot the dark nebula with my Canon XSi and 20-200mm lens, set to 100mm focal length at F/3.2.  Starting with the rear leg of the horse, or the pipe part of the nebula, I shot 10 exposures of 3 minutes each, shifted northward and repeated the sequence for the center and head sections of the field.  I took a couple corresponding dark frames at the start, between fields, and after the sequence to subtract during processing.  One rule-of-thumb in processing is that you sit in front of the computer just about as long as you spend exposing, and it was true in this case too.  Of course, it would help if I did this more often and became a little more proficient...  Luckily the automatic "photomerge" function in Photoshop worked on these starfields and made the mosaic construction easier.

The image at left is the result.  Do click on the image to see the full-size version - reproduced here at the Blog maximum 1600 pixels across.  There are a LOT of deep sky objects contained in the field, including a dozen or so globular clusters, and likely more Barnard cataloged dark nebulae.  The one that is readily seen is B72, the Snake Nebula, located right about in the center of the frame.  Unfortunately, the scale of the image is still too small to resolve many more objects.  I've rotated the frame to better "see" the Prancing Horse shape.  And while the left side of the frame looks redder (and corresponds to the first frame), I've treated all the fields the same, so I believe it is real...

This is the same frame, cropped slightly and rotated back so that North is upwards to show the "Pipe" (as in smoking pipe).  The tendrils are supposed to be wisps of smoke emanating upwards from the pipe.  Let me know if anyone doesn't see the shapes, and I'll add an annotated pair of images...

About the only way to do better, in resolution and depth is to start zooming into the field, particularly with the 1600 pixel blog limit.  It is too late in this observing session to do much of that, but may take up the challenge in the future!

3 comments:

John Dolby said...

Wow! Those Milky Way shots are just stunning. A 200mm camera lens and a tracker seems like the ideal setup; except, that is, for all the work after the shoot! Nice job! But then you always do a nice job.

Anonymous said...

nice "horsie" image, beautiful photos.

Alan Strauss said...

Great shots Dean, I love the panorama!