The bright star just off the left edge in this image
is the far-left star on Orion's belt (zeta Orionis,
also called Alnitak). This star ionizes parts of the
vast hydrogen cloud that spreads throughout Orion;
when the electrons rejoin their atoms, the red glow
seen in this image results. In front of this glowing cloud
is a blob of dust and gas which blocks some of the light.
This dark spot is officially designated as B33, but the
more common and more descriptive name for it is
"the horsehead nebula".

Image data:
Camera: DSI-Pro, hydrogen-alpha filter (false color)
Exposure: 4 minutes x 30
Telescope: William Optics 66mm