Astronomy Picture of the Day -- The Horsehead Nebula

NASA ^ | October 21, 2012 | (see photo credit)

[SunkenCiv]

Explanation: One of the most identifiable nebulae in the sky, the Horsehead Nebula in Orion, is part of a large, dark, molecular cloud. Also known as Barnard 33, the unusual shape was first discovered on a photographic plate in the late 1800s. The red glow originates from hydrogen gas predominantly behind the nebula, ionized by the nearby bright star Sigma Orionis. The darkness of the Horsehead is caused mostly by thick dust, although the lower part of the Horsehead's neck casts a shadow to the left. Streams of gas leaving the nebula are funneled by a strong magnetic field. Bright spots in the Horsehead Nebula's base are young stars just in the process of forming. Light takes about 1,500 years to reach us from the Horsehead Nebula. The above image was taken with the 0.9-meter telescope at Kitt Peak National Observatory.

[SunkenCiv]

[Credit & Copyright: Nigel Sharp (NOAO), KPNO, AURA, NSF]

[SunkenCiv]

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[bigheadfred]

Interesting there are shadows.

Sigma Orionis is an interesting multiple binary, some of whose components can be enjoyed with binoculars.
Sigma is a multiple binary with one very close companion and two wider ones.

What is the difference here between a "multiple binary" and a quaternary star system? Is there no difference except moslems can't count past two?

[TheOldLady]

Pretty horse, as ever. It’s nice that the APOD shows it off every once in a while. Thanks, Civ!