When a star goes supernova, it is a violent and catastrophic event that more often than not outshines the parent galaxy's total light output. Stars in external galaxies that have been witnessed as supernovas have been measured to exceed the Sun's brightness by a billion times. The nebula pictured here is the remains of a star that went SN in the year 1054A.D., as witnessed on Earth. It was so bright, it was visible during the daytime for several weeks. This is the Crab Nebula, also known as M1 in Taurus. It is estimated to be at a distance of 6,500 light years. The speed of light is approximately 300,000 kilometers per second or 186,000 miles per second. It is believed that the most powerful SN's occur due to a companion star's mass being gravitationally drawn to a white dwarf star. When the dwarf's mass exceeds a certain value, it undergoes rapid Carbon burning and explodes, immediately ejecting the equivalent of 1 solar mass (The Sun's mass).