The Orion Nebula - A stellar nursery
HII Regions - Stellar Nurseries
Hidden in the sword of Orion the hunter, a weapon and symbol of death, lies the birthplace of new stars - the stunning Orion Nebula, one of the many objects catalogued by Charles Messier in the 18th century during his hunt for comets. Messier noted the position of the nebula because he didn't want to mistake it for a comet. Too bad he didn't notice the spectacular event taking place in the nebula, which he named M42. Nestled in the center of M42 is a group of stars, known as the Trapezium, which have formed from the gas in the nebula.
From their spectra, we can determine that these stars are blue and hot. We can determine the distance to these stars and thus figure out that they are quite bright. The theory of stellar evolution tells us that hot, bright, blue stars are very young. So by studying the stars in the centers of objects like the Orion Nebula, we realize that HII regions are the birthplaces of stars.
The Orion nebula is more or less circular in shape, and it glows with a characteristic red color. All these types of stellar nurseries, called HII regions, have this color. There are many HII regions with young stars in the disk of our Galaxy.