We had our first guests at our Cabin in the Sky on the weekend of June 18-20 2010, Mehrdad and two of his girls, Roxanna and Avesta! John and his wife Karen also visited Sunday afternoon.

That Friday night and into dawn on Saturday morning Mehrdad helped me frame the following image of the Cocoon Nebula, IC 5146, also known as Caldwell 19. This lovely object lies in a star-jeweled region of the Milky Way in Cygnus. It brings to mind a galactic pink-red wild rose! It has been on my imaging list for over two years, since I first read about it in Stephen O'Meara's book The Caldwell Objects. I've been fascinated by its gorgeous colours and textures, with hints of blue reflection nebulae bordering the red emission region, and with a dark dust lane, cutting across this frame from top-right to middle-left, obscuring background stars. The brilliant stars of many colours crowding the bottom-right corner of this frame give the impression of having been swept there by the dark lane.

Our imaging session had to wait until about 12:30AM for the Moon to set, which reduced the already short amount of time available to us before astronomical dawn. We had planned to image the Cocoon for a second night on Saturday, but a problem with the camera (which turned out to be frost on the chip) meant that I had to be content with another single evening with a short integration time, in this case of just 100 minutes LRGB total. The individual frames were 10 minutes each in L unbinned, and 5 minutes each in R, G, and B (with 2x2 binning). Image capture and initial processing were done with MaxIm DL, with additional processing under Photoshop. Seeing conditions were about 2.5" HFD, and the image scale is 0.75" per pixel (thanks to a 0.66x PlaneWave focal reducer). The field of view is nearly half a degree!

I also finally got FocusMax working this weekend. This software is every bit as good as what I've read. The algorithm is very clever, using far out-of focus stars to extrapolate to the correct focus position, with the star "size" being measured by integrals over the flux distribution, yielding the so-called half-flux diameter (HFD), rather than from an direct estimate of the width of the distribution (such as the full-width at half-maximum, which is not as useful a measure when the star is so far out of focus that it has a donut shape, due to the shadow caused by the secondary mirror). An advantage of using far out-of focus stars is that their "size" is very insensitive to fluctuations caused by atmospheric turbulence. This produces a much more robust determination of the correct focus position than the more obvious method of trying to measure near the best focus, where atmospheric fluctuations can produce wild variations in readings. The automated wizard made calibration of the software a snap, and its robustness was clear even from the limited testing I did this night, before shooting the Cocoon.

CITSO Blog: The Cocoon Nebula,
a galactic pink-red wild rose, June 18/19 2010

Copyright © 2014 Howard Trottier