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 nebula on right bottom to the center
, and colorful M20 above. The third, NGC 6559, is at left of 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.
[Text adapted from APOD]