by APOD Robot » Tue Dec 31, 2013 5:05 am
The Horsehead Nebula
Explanation: The
Horsehead Nebula is one of the most famous nebulae on the
sky. It is visible as the dark indentation to the red
emission nebula in the center of the above photograph. The
horse-head feature is dark because it is really an opaque
dust cloud that lies in front of the bright red
emission nebula. Like clouds in
Earth's atmosphere, this cosmic cloud has assumed a
recognizable shape by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission
nebula's red color is caused by
electrons recombining with
protons to form
hydrogen atoms. Also visible at the bottom left of the picture is a greenish
reflection nebulae that preferentially
reflects the blue light from
nearby stars.
[/b]
[url=http://apod.nasa.gov/apod/ap131231.html][img]http://apod.nasa.gov/apod/calendar/S_131231.jpg[/img] [size=150]The Horsehead Nebula[/size][/url]
[b] Explanation: [/b] The [url=http://en.wikipedia.org/wiki/Horsehead_nebula]Horsehead Nebula[/url] is one of the most famous nebulae on the [url=https://www.facebook.com/APOD.Sky]sky[/url]. It is visible as the dark indentation to the red [url=http://apod.nasa.gov/apod/emission_nebulae.html]emission nebula[/url] in the center of the above photograph. The [url=http://apod.nasa.gov/apod/ap070527.html]horse-head[/url] feature is dark because it is really an opaque [url=http://apod.nasa.gov/apod/ap030706.html]dust[/url] cloud that lies in front of the bright red [url=http://fusedweb.pppl.gov/CPEP/Chart_Pages/5.Plasmas/Nebula/Emission.html]emission nebula[/url]. Like clouds in [url=http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html]Earth's atmosphere[/url], this cosmic cloud has assumed a [url=http://www.brucevanpatter.com/cloudshapes.html]recognizable shape[/url] by chance. After many thousands of years, the internal motions of the cloud will alter its appearance. The emission [url=http://apod.nasa.gov/apod/ap061015.html]nebula[/url]'s red color is caused by [url=http://www.pbs.org/transistor/science/events/electron.html]electrons[/url] recombining with [url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/proton.html]protons[/url] to form [url=http://periodic.lanl.gov/1.shtml]hydrogen[/url] atoms. Also visible at the bottom left of the picture is a greenish [url=http://apod.nasa.gov/apod/reflection_nebulae.html]reflection nebulae[/url] that preferentially [url=http://spaceplace.nasa.gov/blue-sky/en/]reflects the blue light[/url] from [url=http://apod.nasa.gov/apod/ap010318.html]nearby stars[/url].
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