The Crab Pulsar, a 16-mile-wide (26 kilometers) star remnant that exploded in approximately 5450 b.c., spins 33 times per second. It sits in the center of this X-ray and optical-light image of the Crab Nebula. The story of the Crab Nebula (M1) really started before dawn July 4, 1054, when a dazzling new star abruptly appeared near the left horn of Taurus the Bull. As bright as Venus, it could be seen in broad daylight for weeks. It was duly noted by observers in China and duly ignored in the West, where alterations in the heavens were hard to reconcile with the prevailing theology. Centuries later, our telescopes revealed this object as the remnant of an exploded star 6,500 light-years away, whose tendrils still rush outward at 1,000 miles (1,600 kilometers) a second, visibly altering the nebula every few years.