Lunar eclipse and Orion Nebula
Name: Andrew G Cantrell
1) Is the Moon ever truly full except during a total solar eclipse?
2) Is there a reason that the orion nebula appears blue in my telescope?
1) No, the Moon cannot be full during a solar eclipse!
[perhaps you were thinking of lunar eclipses?]
2) The Orion Nebula is one of the brightest of the emission nebulae or H II
regions (the "H II" means ionized hydrogen). Emission nebula are usually
reddish because they fluoresce by converting stellar UV radiation into the
hydrogen Balmer lines, especially H-alpha which is in the red region of the
visible spectrum. Why it appears blue could be due to many reasons having
to do with your telescope, atmospheric conditions, Orion's elevation above
the horizon, or it might actually be blue because of the presence of oxygen
in the nebula. [for those who do not know, the Orion Nebula is the middle
"star" of the three making up "The Hunter's" sword hanging from his belt...]
AHA! There is a small cluster of 5 blue stars inside the nebula.
Reference: Whitney's Star Finder by C. A. Whitney, Alfred A. Knopf, 1977;
a great little book for anyone interested in viewing the night sky; includes
info on eclipses, sunrises and sunsets, comets, meteors, auroras, rainbows,
haloes, sundogs, and how to photograph all these.
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Update: June 2012