This is essentially the gas cloud (“nebula” means “cloud”) left over from a supernova explosion in A.D. 1054. The Chinese noted this event as being so bright that it was visible during the day for several weeks. Since then, it has gradually expanded, cooled, and become dimmer. The center of the cloud contains a tiny neutron star, about 20 miles across, which rotates about 30 times per second and emits gamma rays. You don’t want to get too close to this type of radiation, but it’s OK in this case, as the nebula is about 6,500 light-years away. The photo was taken with an ordinary camera, but with a 5-minute exposure time.
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