These three bright nebulae are often featured in telescopic toursof the constellation Sagittarius
and the view toward the center
of our Milky Way galaxy.In fact, 18th century cosmic tourist Charles Messier
cataloged two of them; M8, the nebula above and left of center,and colorful M20 at the lower left.The third, NGC 6559
, is at the right of M8, separatedfrom the the larger nebula by a dark dust lane.All three are stellar nurseries aboutfive thousand light-years or so distant.The expansive M8, over a hundred light-years across,is also known as the Lagoon Nebula
while M20's popular moniker is the Trifid
.In this gorgeous digital composition
,the dominant red color of the emission nebulae is dueto glowing hydrogen gas energized by the radiation of hot,young stars.The contrasting blue hues, most striking in theTrifid as well as NGC 6559, are due to dust reflected starlight .
Selected NASA's Astronomy Picture the Day for September 9, 2004.