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NGC 7822 is a large, complex emission nebula and star-forming region, filled with hot young stars recently formed from and heating its gases, and partially obscured by dark lanes of gas and dust lying between us and the brighter emission region. The emission nebula covers at least 3 degrees, which at its distance of nearly 3000 light years makes it 150 light years across. The loose cluster (or association) of stars near its center contains about 40 O and B stars, of which type O7 is the "earliest", or hottest. This implies an age of 5 to 6 million years for the association.
Credit: Davide De Martin & the ESA/ESO/NASA Photoshop FITS Liberator/Digitized Sky Survey 2