The unusual nebula NGC 7635 in Cassiopeia. Often called the Bubble Nebula, this object is sometimes misclassified as a planetary nebula. POSS/DSS photo.

This month's deep sky object is slightly more challenging than last month's object. NGC 7635, also known as the Bubble Nebula, is a somewhat faint glow located only half a degree from M52 in Cassiopeia. Dark skies are mandatory; a six-inch or larger telescope and a UHC (or similar) filter will probably be needed for a good view.

The nebula appears as a well-defined glow about 2.5 arc-minutes across. The glow is somewhat comma-shaped with the head to the west of a bright star. The glow dims and narrows as it sweeps around to the east. In a 12.5" scope, I saw no traces of the faint arc that completes the circle. The "comma" is embedded in a faint band of nebulosity about 10 x 3 arc-minutes in size and running roughly northwest-southeast.

The Bubble is pretty much what it looks to be. Stellar winds from a massive star have blown out the surrounding gas into a thin shell, while radiation from the star causes the gas to glow. The nebula is 11,300 light-years away and is about 10 light-years across.

How to get there:

NGC 7635 is slightly north of the midpoint between Beta Cassiopeiae and Delta Cephei. The open cluster M52 is only half a degree away.

Finder chart for NGC 7635