The Crab Nebula is the remnant of a tremendous stellar explosion witnessed by Chinese astronomers in 1054. The explosion, called a supernova, occurred at a distance of about 2000 parsecs from the Earth (1 parsec = 1.9 × 10¹³ mi = 3.1 × 10¹³ km = 3.26 light-years). Even so, it was bright enough to be visible in the daytime sky for 3 weeks and in the nighttime sky for 2 years.