Ask A Scientist© Astronomy Archive

Question:  Is the moon ever truly full except during a total solar eclipse?
Is there a reason that the oion nebula appears blue in my telescope?
andrew g cantrell

Answer 1:  
1) nope, the moon can't be full during a solar eclipse! (why?)
   [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 don't know, the Orion Nebula is the middle "star" of the
three making up "The Hunter's" sword hanging from his belt...

Answer 2:  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 viweing the night sky;
includes info on eclipses, sunrises and sunsets, comets, meteors,
aurorae, rainbows, haloes, sundogs, and how to photograph all these.
hawley