Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

August 10, 1997

Nebulosity in Sagittarius
Credit & Copyright: D. Malin (AAO), AATB

Explanation: What causes the colors in this beautiful nebulosity in Sagittarius? Dubbed NGC 6589 and NGC 6590, the colors of this nebulosity, are caused by gas and dust. The blue color of the nebula nearest the bright stars is caused by reflection off interstellar dust. The dust emits little visible light of its own - in the absence of a nearby star the dust would appear dark, blocking light from background stars. The red color of the nebula furthest from the bright stars is caused by glowing hydrogen gas. Energetic light from the central stars ionizes hydrogen gas - which glows red when recombining with a local electron.

Tomorrow's picture: A Perseid Meteor

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