The Crab Nebula is the remains of a supernova that exploded July 4, 1054 AD.  Actually, it was observed by the Chinese as a new, bright star on that date, but since we now know that it was a supernova located 6000 light years away it actually exploded at about 5000 BC and the light from the explosion merely reached us in 1054 AD.

The filamentary nebulosity is about 9 'arc across in this 14 'arc wide unfiltered image of the Crab Nebula.  [Meade LX200 10-inch SCT, clear filter, 416XTE CCD; 260-seconds worth of exposures from 2001.11.07/08 & 2001.11.14/15; Santa Barbara residence.]

Color version, created by combining red, green and blue images to the unfiltered image above (using the RGBL technique for creating color pictures from a set of filtered images).  [Same observing equipment; combining 80-seconds worth of red, green and blue exposures with 260 second's worth of unfiltered exposures using the RGBL technique for creating color images from filtered and unfiltered observations; 2001.11.14/15 and 2001.11.07/08].

A supernova differs from a nova in a significant way.  A supernova explodes when it becomes unstable after consuming hydrogen at the star's center.  An implosion is followed by an explosion, blasing most of the star's material outward.  With most of the star's mass lost to space, the remaining core collapses further to a neutron star, spinning fast due to the "ice skater" effect (conservating angular momentum during the collapse).  (At the center of the Crab Nebula is neutron star rotating 30 times per second, referred to as a "pulsar.")  The escaping, outward-moving material is luminous due to its encounter with interstellar material.  A supernova is a one-time event for the star that explodes, and its inherent brightness is immense.

A nova, on the other hand, is one star of a binary pair that has stallar material "dumped" on it by its companion, and the infalling material briefly raises the temperature of the surface and creates an outpouring of light energy which gradually subsides.  The same nova may undergo repeated outbursts, as it is never destroyed by any of its brightenings.  A nova is a repeating event for the affected star, and its brightness for each event is inherently much less than for that of a supernova.

This site opened:  November 15, 2001.  Last Update:  November 20, 2001