Caption: The French astronomer Charles Messier (1730-1817) listed over 100 objects he saw as nebulous to avoid confusing them with comets, which were his main interest. Three of Messier's objects appear in this picture. A little below the bright red emission nebula M17 is M18, a group of stars which is only conspicuous because, like M17, it is set in a relatively dark region of the Milky Way. The rich cloud of stars more or less in the middle of the photograph was listed by Messier as number 24 in his catalogue and it contains the open cluster NGC 6603, while towards the bottom of this field is a small group of nebulosities that Messier either did not see or which he considered to be too faint to interfere with his comet seeking. These are the two blue reflection nebulae NGC 6589-90 and the emission nebulae IC 1283-4.
