Cygnus Loop -- "The Aftermath of a Star Blowing Itself  Asunder"
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This image, taken with the HST's Wide Field and Planetary Camera 2, shows a
region of gas and dust about 2500 light years away  in the constellation
Cygnus,
the Swan (which is high overhead in late summer).  The glowing gas is the
result
of a shock wave from an exploding star, or supernova, that occurred about
15,000
years ago.  The blast wave is moving through the cloud, compressing  and
heating
the gas and so is causing it to glow.   If the gas in this image was bright
enough to be seen by the naked eye, it would cover an area in the sky 
equal to
about 6 times the area of the full moon.
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