The Bubble Nebula (NGC 7635) is an emission nebula in the constellation Cassiopeia: a delicate, almost perfectly round shell of glowing gas blown into space by a single massive star. This wide field also includes the emission nebula NGC 7538 on the left and the open star cluster M52 on the right.
The Bubble Nebula lies about 7,100 light-years away and spans roughly 10 light-years; the powerful wind of the hot young star at its edge pushes the surrounding hydrogen outward and makes it glow. NGC 7538, just across the border in Cepheus, is a region where massive stars are being born, while M52 is a rich open cluster of young stars about 5,000 light-years away. Both nebulae were discovered by William Herschel in 1787.
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