The Crab Nebula
August’s Space Object of the Month is the Crab Nebula, the remnant of a supernova observed by Chinese astronomers in the year 1054. Though they didn’t understand what they were seeing at the time, we now know they were witnessing was the death of a star 6,500 light-years from Earth. The supernova was visible during the day for an entire month, and remained visible at night for a further two years before it faded away.
At the centre of the nebula there is a rapidly spinning neutron star, 30 kilometres in diameter, emitting pulses of radiation as it spins on its axis. This pulsar, discovered in 1968 by Jocelyn Bell, ejects twin beams of radiation resulting in the star appearing to pulse at a rate of 30 times per second.
The nebula itself spans six light-years across, and is expanding at a rate of about 1,500 kilometres per second – 0.5% the speed of light.
