The Crab Nebula is the remnant of a star that exploded as a supernova in 1054 A.D. The supernova was visible in the daytime for 23 days, shining four-times brighter than Venus. The supernova was visible to the naked eye in the night sky for almost two years before fading out. What we see today is the gaseous material ejected by the exploding star. This material is moving outward from the nebula's center at 1,800 kilometers (1,080 miles) per second. At the nebula's core is an extremely dense neutron star or pulsar, which rotates 30 times per second.

Astronomer Charles Messier observed the Crab Nebula in 1758 while searching for Comet Halley. This was the inspiration for Messier to develop a list of all celestial objects that might be mistaken for comets—the Messier catalog. The Crab Nebula is the only supernova remnant in the Messier catalog.

The Crab Nebula can be a disappointing object for stargazers. Look for a dim, elongated glow in a small telescope or good binoculars. A network of fine filaments can be glimpsed with a large telescope under dark skies and averted vision. Discern the classic "S" shape of the nebula's central region. The central pulsar is, of course, tiny and is not visible.

Click here to see if this object is visible in your sky tonight.