Dark Horse Observatory
Image Details: NGC 2403
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Nestled in a dark northern cave in the sky surrounded by Cassiopeia, Perseus, and Auriga, Camelopardalis (the giraffe) shares this cave with the two bears and a lynx (this cave is more like a zoo!). This constellation is all but hidden from naked eye detection for most observers in the currently light-polluted skies. It has no stars brighter than 4th magnitude, but spans 757 square degrees which makes it the 18th-largest constellation. Hidden in this faint constellation are several treasures including a faint, beautiful, spiral galaxy, IC 342 (Caldwell 5) which is obscured by the dust clouds of our own galaxy because it is only 11°above the plane of our galaxy. It also contains NGC1501, a nice planetary nebula with a central star, and NGC1502 which is a compact open star cluster.
NGC2403, a mixed spiral galaxy, is 23.8’ by 12.8’ in size and has a surface brightness of magnitude 7.3. It is located near the nose of the Great Bear, Muscida. It is almost 8° away from this star in a direction almost parallel to the meridian. NGC2403 is located 12 to 14 million light-years away from Earth. NGC 2403 is an outlying member of the M81 group and it is a member of the Coma-Sculptor Cloud of galaxies. This gravitationally bound system also includes our local group and spans 90,000 light years of space.
Historically, this was first discovered in 1788 by William Herschel. Another contribution to the science of astronomy is that NGC2403 is the first system beyond our local group where Cepheids (variables whose periodicity has been an important tool for measuring extragalactic distances) were identified. When seen from Earth, the galaxy is inclined 28° from edge on. On first appearance the face of the galaxy seems to have clumps of starlight which could be misinterpreted as supernovae. Some of these are foreground stars, but other clumps of light were identified by Edwin Hubble during the 1950s using the Palomar Mountain 200-inch reflector as being over 100 H II regions lining the galaxies spiral arms. The largest of these has its own NGC denomination, NGC2404, and is locate 6’ north-northeast of the nucleus. It has an apparent diameter of 20” which means that it has a true diameter of 1,400 light-years!
When I decided to image this galaxy, it was the large number of H II star-forming regions that captured my interest. The only reference images I had were those done by much larger telescopes including an amazingly detailed image by Robert Gendler with his 20-inch RC from New Mexico. These were not challenges that I could easily meet with my 10 inch BRC-250 under suburban Philadelphia skies, not to mention that this was my first foray into any form of color imaging. Undaunted, ignorance is a wonderful thing (ignorance is bliss is the expression that comes to mind) I tried to capture this galaxy.
North on this image is located to the right and somewhat down. I hope that you enjoy this first effort into color imaging. I have subsequently reprocessed it as my skills became greater.
SEDS link for additional information: http://www.seds.org/messier/xtra/ngc/n2403.html