Emission Nebula
A cloud of ionized gas emitting light of various colors, often found in regions of active star formation and contributing to the reddish hues observed in galaxies.
Source: esa.int
APODs including "Emission Nebula"
Southwest Andromeda
17/09/2001
This new image composite of the southwest region of M31 from the Subaru Telescope shows many stars, nebulae, and star clusters never before resolved. An older population of stars near Andromeda's center causes the yellow hue visible on the upper right. Young blue stars stand out in the spiral arms on the lower left. Red emission nebula, blue open clusters of stars, and sweeping lanes of dark dust punctuate the swirling giant. Andromeda, at about 2.5 million light years distant, and our Milky Way are the largest galaxies in the Local Group of Galaxies. Understanding M31 helps astronomers to understand our own Milky Way Galaxy, since the two are so similar.