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.

March 12, 1996

The Colourful Clouds of Rho Ophiuchi
Credit: Photograph made from plates taken with the UK Schmidt Telescope. Colour photography by David Malin. Copyright: Royal Observatory, Edinburgh, Anglo-Australian Observatory

Explanation: The many spectacular colours of the Rho Ophiuchi (oh'-fee-yu-kee) clouds highlight the many processes that occur there. The blue regions shine primarily by reflected light. Blue light from the star rho Ophiuchi and nearby stars reflects more efficiently off this portion of the nebula than red light. The Earth's daytime sky appears blue for the same reason. The red and yellow regions shine primarily because of emission of the nebula's atomic and molecular gas. Light from nearby stars - particularly the bright star Antares in this case - knocks electrons away from the gas, which then shines when the electrons recombine with the gas. The dark regions are caused by dust grains - born in young stellar atmospheres - which effectively block light emitted behind them. The Rho Ophiuchi star clouds, well in front of the globular cluster M4 visible on far lower left, are even more colourful than humans can see - the clouds emits light in every wavelength band from the radio to the gamma-ray.

Tomorrow's picture: Here Comes Comet Hyakutake

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
&: Michigan Tech. U.