Horsehead Nebula in hydrogen alpha (Ha). Taken with a full spectrum modified Canon 60D.
C102/f5 achromat. Ha is a particular wavelength of light produced by unionized hydrogen
(and even non-union hydrogen....) at the far end of the red spectrum of light that is
unaffected by light pollution and less affected by atmospheric turbulence than more
visible light. This makes it a viable method of astrophotography for folks living in
highly light-polluted areas.