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NGC 2403 (Caldwell 7)


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About this observation
Dr Ollie Garrett
Time of observation
29/03/2019 - 21:07
NGC 2403 (Caldwell 7)
Observing location
Dartmoor, UK
115mm f7 APO refractor
NEQ6 mount
SX Lodestar and SX OAG
Baader 36mm filters
L: 5x300s, R: 7x300s, G: 7x300s, B: 6x300s
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The subframes for this image were gathered between 20:34 UT on 29-3-19 and 00:51 UT on 30-3-19. Conditions were favourable throughout with fairly good seeing and good transparency. Sky darkness was measured at 20.10 magnitudes/arcsecond squared at 21: 07 UT (29-3-19) and improved to 20.85 magnitudes/arcsecond squared at 01:14 UT (on 30-3-19). 

The luminance stack is a little smaller than intended as several frames were affected by aircraft trails and not included in this processing sequence.

Despite its huge diameter of about 50,000 light years, the apparent size of this galaxy is quite small for my imaging system - a result of NGC2403 being located approximately 8 million light years away! Despite the challenges with image scale, I'm pleased with the resolution in the image of several of the largest star-forming regions distributed along the spiral arms of the galaxy. At some point, I'll return to this target to capture a set of subframes in Hydrogen alpha. This should add some more detail to the rendition of the HII regions in the image.

Interestingly, Kepple and Sanner's The Night Sky Observer's Guide notes that NGC2403 has the distinction of being the first galaxy beyond the Local Group in which a Cepheid star was discovered (by Allan Sandage using the Hale telescope).

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