Coming Full Circle

September 28, 2020  •  1 Comment

Veil NebulaVeil NebulaThe Veil Nebula, aka Cygnus Loop, the remnant of a long ago supernova explosion. A composite of 22 frames 90 sec. each, f/7.1, ISO 6400, Nikon D800, modified for sensitivity to hydrogen light, tracked with an iOptron CEM25P mount. Processed in Lightroom and combined in Starry Sky Stacker. Recently I've been trying to take more detailed images of celestial landscapes, concentrating on a middle ground between wider views that juxtapose earth-bound landscapes with the night sky, and very deep, detailed images of distant heavenly bodies. The equipment I've been using isn't ideal for deep sky astrophotography of objects that are faint and small in angular size. But it works nicely to photograph regions of the sky that include extended objects like large star-forming nebulae, the nearest galaxies, the occasional comet cruising by the Earth or in this case the result of a supernova explosion. Of course these are not the exquisitely detailed images made by the Hubble Space Telescope and other research instruments. But their cameras can't easily take in these vast expanses of the universe. (See the previous blog entry about fields of view.)

One of the objects I was able to photograph not long ago is the Cygnus Loop (also known as the Veil Nebula), the remnants of a star in our Milky Way Galaxy that blew itself apart in a titanic supernova explosion a long time ago. One of the reasons I wanted to make this picture was some connections I have with this target. For one, I helped produce one of the Hubble images of this object. It's just a teeny-tiny part of the enormous region, but reveals the exquisite structure at all its physical scales.

Veil NebulaVeil Nebula from the Hubble Space Telescope

Another reason I pursued this goes back exactly 50 years to my first college astronomy class in the Fall of 1970. The textbook we used was Exploration of the Universe by George Abell and on the cover was a picture not too different from mine, a zoom-in showing only one section of the full area, the left region of nebulosity but in greater detail. And yes, I still have the book, one of the best textbooks I had and one I've referred to many times over the years. Also note the vintage punch cards used as bookmarks — originally, input to the CDC 6600 mainframe computer I used in college. I think that might be a line of COBOL! 

I don't know all the details of that cover image, the caption only refers to the source as Mt. Wilson and Palomar Observatories. I'd guess it was made in the 1960s, certainly from monochrome glass plates, likely using the 48-inch Schmidt telescope on Mt. Palomar. It may have been assembled from images used to produce the comprehensive all-sky survey known as the Palomar Observatory Sky Survey (POSS). These are wide-field (about 6º square) photographs originally taken in two colors covering the whole sky as seen from Southern California.  The color image from Palomar would have been made painstakingly in the darkroom by combining copies of the plates taken through different filters, rather unusual at the time before much more convenient digital photography. Looks like the last edition of the textbook was in 1995, and sports a great photo of the Hubble Space Telescope on the cover. 

The POSS was revolutionary in astronomy and used extensively, not only as a guide to more detailed observations but as a research tool in itself. In fact one of George Abell's greatest accomplishments (besides writing one of the most-used astronomy textbooks) was the systematic cataloguing of clusters of galaxies using the POSS plates. But even beyond that, the POSS was digitally scanned and used to compile a catalog containing millions of stars with very precisely measured positions and brightnesses used to very accurately point the Hubble Space Telescope: the Digitized Sky Survey and Guide Star Catalog. Subsequently, later generations of plates were taken with improved technology and additional filters to extend and refine the images and catalogs derived from them.

Now I can turn my off-the-shelf — albeit high-end — thoroughly modern digital SLR camera to the same spot in the sky and make what I consider a respectable photograph of the same subject. Sure it's not the equal of an image made by a gigantic telescope on huge pieces of sensitized glass (or even by more sophisticated backyard astrophotographers) but I think it's a beauty: filled with stars and showing colors of ionized gases in clouds energized by the long-ago explosion of a dying star. So I feel I've come full-circle in some respect, with a few twists and turns along the way — the (sort of) circular Cygnus Loop is something of a metaphor for me then: a beautiful celestial object now bringing to mind many aspects of my life.


Chris Woakes(non-registered)
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