Similarly, to sail west at a constant latitude Columbus kept the north star at a constant altitude above the horizon. The size of each star indicates its relative magnitude . Constellation names are light blue . Messier object numbers are pink . Globular clusters are gold starbursts .
Open clusters are dotted white circles.
Planetary nebula are green diamonds . Bright nebula are magenta squares . Dark nebula are grey rectangles . Green x's are x-ray sources. Purple O's with a diagonal slash through them are quasars.