NGC 6946 – Spiral Galaxy in Cepheus

NGC 6946. Image: Rense Boomsma

NGC 6946. Image: Rense Boomsma

A mere 40 arcminute hop from last month’s Sky Object (the open cluster NGC 6939) takes you 5000 times deeper into space to the face-on spiral galaxy NGC 6946. NGC 6946 was discovered by William Herschel on the same night – September 9, 1798 – that he notched NGC 6939.

Most sources assign to NGC 6946 a visual magnitude of 8.9. Don’t be misled by this seemingly “bright” figure. As is the case with similar face-on galaxies like M33 and M74, the light is spread across a wide area (in this instance, 11 by 10 arcminutes), resulting in a very low surface brightness. Working with a 10-inch reflector on a recent evening, I could barely glimpse NGC 6946 as “a large, circular glow (averted vision only).” The limiting magnitude that night was 5 – not exactly a pristine condition. If you want to spot NGC 6946 with a small-aperture scope or tease out any kind of structural detail with a big Dob, you’ll want to work under clear, magnitude 6 or better skies.

NGC 6949 has been nicknamed, the “Fireworks Galaxy.” The moniker is appropriate. Since 1917, nine of its stars have erupted as supernovae - the last in 2008. This is an amazing figure when you consider that NGC 6946 is about half the size of our Milky Way Galaxy.

Glenn Chaple
Glenn Chaple
Entry Date:
Oct 22, 2013
Published Under:
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