Distance: 5,200 light-years (1.6 kpc) Image Size = 18 x 18
arcmin Visual Magnitude = 9.0  Ultraviolet Image Not Available
X-Ray: ROSAT   Visible: DSS Visible: Color NOAO/AURA  Messier 20
is more commonly known as the Trifid Nebula and is a favorite
photographic target of amateur astronomers.   We begin our tour
by examining the spectacular color image (above), where the
Trifid Nebula is revealed by its reddish glow. Messier 20 is an
emission nebula and the reddish color is produced by the
characteristic light of (fluorescent) hydrogen gas. One of the
photographic filters used to obtain this image is tuned to match
the wavelength of the hydrogen gas, partly explaining why M20 is
reasonably bright in this picture. A bright star cluster lies at
the center of the emission nebula, and is partially obscured by
lanes of thick dust. These dust threads are dark because they
obscure visible light, and are consequently seen in silhouette
against the brighter background.  The blue reflection nebula to
the north is unconn