The Crab Nebula is the remnants of a star which as exploded as a supernova in the year 1054. It is located around 6500 ly away and the brightness at the time of the supernova would have been 400 million times that of the Sun - it appeared on Earth as bright as a quarter Moon. At the centre of the nebula is a neutron star which is so dense that a piece of its material the size of a matchbox would weigh 2000 million tonnes. It spins some 30 times per second giving rise to a pulsar which emits copious amounts of x-rays. At magnitude 9, large binoculars and dark skies are required to see it.