The nebula M17, in the const- ellation Sagittarius, is about 5,000 light years away. Among the brightest of the many gaseous nebulae in the sky, it is easily observed, even through small telescopes. This visible light image shows only the inner 12 light years of M17ΓÇöthe portion most easily seen by telescopesΓÇöbut longer exposures show the nebula to extend for over 40 light years.
The red coloring is generated by the H alpha emission of hot hydrogen gas, although other glowing gases are also present. The dark areas are clouds of dust that have mixed with the gases. In particular, the ΓÇ£holeΓÇ¥ on the top is caused by small dust particles, compounded across light years, obscuring the bright gases. The
