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January 2002

The Crab Nebula

In the year 1054, Chinese astronomers reported a "guest star" that rapidly grew in brightness. Within a few days of its discovery, it was brighter than the full Moon, and remained visible in the daytime skies for months. What they saw was a supernova - the spectacular demise of a star many times more massive than our Sun. Such stars explode when they run out of nuclear fuel. The cataclysmic explosion spews heavy elements into space, which later can be incorporated into new stars and planetary systems.

Most of the carbon, oxygen, calcium, iron, and other elements that make up our world (and us) were produced in the cores of long-dead stars, like the 1054 supernova but billions of years earlier. These elements slowly made their way through the galaxy to become part of our solar system.

The Crab Nebula is all that remains of the supernova of 1054. It is an expanding mass of glowing hydrogen and helium gas, but with significant amounts of heavy elements. Visible through binoculars as a faint smudge at the tip of one of the horns of Taurus, CCD imaging reveals knotted filaments as well as the remnant core of the star within the bright bluish central patch. This nebula lies about 6300 light years from Earth.