Comet over California

Still gracing northern skies, a fading Comet Holmes lies at the top edge
of this colorful skyview, recorded on March 4. The reddish emission nebula
below it is NGC 1499, also known as the California Nebula for its resemblance
to the outline of the state on the US west coast. Of course, the two cosmic
clouds by chance lie along nearly the same line-of-sight and so only appear to
be close together and of similar size. The California Nebula is actually about
100 light-years long and 1,500 light-years away, drifting through the Orion Arm
of our spiral Milky Way Galaxy. Comet Holmes is about 20 light-seconds in
diameter,sweeping through our solar system a mere 25 light-minutes away, beyond
the orbit of Mars. The molecules of the comet's gaseous coma fluoresce in sunlight.
The California Nebula's glow is characteristic of hydrogen atoms recombining with
long lost electrons, originally stripped away (ionized) by ultraviolet starlight.
Providing the energetic starlight is Xi Persei, the prominent star below the nebula.