Discover the cosmos! Each day a different image or photograph of
our fascinating universe is featured, along with a brief
explanation written by a professional astronomer. 2007 February
13 Explanation: The explosion is over but the consequences
continue. About eleven thousand years ago a star in the
constellation of Vela could be seen to explode, creating a
strange point of light briefly visible to humans living near the
beginning of recorded history. The outer layers of the star
crashed into the interstellar medium, driving a shock wave that
is still visible today. A roughly spherical, expanding shock
wave is visible in X-rays. The above image captures much of that
filamentary and gigantic shock in visible light, spanning almost
100 light years and appearing twenty times the diameter of the
full moon. As gas flies away from the detonated star, it decays
and reacts with the interstellar medium, producing light in many
different colors and energy bands. Remaining at the center of
the Vela Supernova Remnant is