Explanation:
These three bright nebulae are often
featured in telescopic tours of the constellation
Sagittarius and the crowded starfields of
the central Milky Way.
In fact, 18th century cosmic tourist
Charles Messier
cataloged two of them; M8, the large nebula left of center,
and colorful M20 on the right.
The third, NGC 6559, is above M8,
separated from the larger nebula by a dark dust lane.
All three are stellar nurseries about
five thousand light-years or so distant.
The expansive M8, over a hundred light-years across,
is also known as the Lagoon Nebula.
M20's popular moniker is the Trifid.
Glowing hydrogen gas creates the dominant red color of the
emission nebulae, with contrasting blue hues, most striking in the
Trifid, due to dust reflected starlight.
This broad skyscape also includes one of Messier's
open star clusters,
M21,
just above and right of the Trifid.
