NGC 6946 (Arp29) & NGC 6939 (Gary Imm)

NGC 6946 (Arp29) & NGC 6939

This image captures a rare part of the sky where two major sky objects are in close proximity (40 minutes apart). The open cluster NGC 6939, located 5,000 light-years away in the constellation of Cepheus, is at the upper left. The spiral galaxy NGC 6946 (the Fireworks Galaxy), located 20 million light-years away on the border of the Cepheus and Cygnus constellations, is at the lower right. Our line of sight in this direction crosses through dense foreground stars and dust regions on the edge of the Milky Way.

NGC 6946 is called the “Fireworks Galaxy” because so many supernovae have been spotted there in the last hundred years. Nine supernovae have been observed in the galaxy’s spiral arms in the past century, more than any other galaxy. The last one was just spotted in May, 2017. The average rate for supernovae in our own Milky Way galaxy is about 1 per century, but we haven't had one for over 400 years so we are overdue. The galaxy contains two bright fuzzy blue knots in the arms, one towards the top of the galaxy and one towards the bottom, which are each comprised of many star clusters.

NGC 6939 has a nice mix of blue and orange stars. The cluster is famous for having two linear chains of bright stars, which emanate from the brightest (11.4 magnitude) star in the cluster at a right angle. This blue origination star is to the top right of the cluster, and the lines extend from this star at angles of 4 o'clock and 7 o'clock. These linear star patterns are easier to see through the eyepiece, where the fainter stars aren't visible to mess up the pattern.

The most interesting part of this image to me is the kite asterism, formed by the four 10th magnitude stars which frame the star cluster in a diamond shape. The tail of the kite extends as a ribbon of stars to the right.

Open Star Clusters
The refractors!
Cloudy Nights
Arp's Peculiar Galaxies
ZWO ASI1600MM/QHY163M

Face-on Galaxies
Many Galaxy Arms
Open Clusters
Secret Deep Catalog (Complete)
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Status	Advanced success
Started	...
Astrometry.net job	2272195
PixInsight job	29JIJ7D9BJOHTUP22OT6TBTNOSPSHTDR
PixInsight queue size	n/a
PixInsight stage	n/a

RA (center)	20h33m20s.179
RA (top/left)	20h30m16s.444
RA (top/right)	20h30m52s.545
RA (bottom/right)	20h36m19s.435
RA (bottom/left)	20h35m52s.302

Dec (center)	+60°24′11″.31
Dec (top/left)	+60°50′43″.74
Dec (top/right)	+59°54′28″.75
Dec (bottom/right)	+59°57′18″.83
Dec (bottom/left)	+60°53′42″.14

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