Towards the end of the long life of many low mass stars, some similar to the Sun, internal changes occur which cause them to shed most of their outer layers of gas, leaving behind a tiny, hot star.
Many stars puff off their gas in a spherical shell.
The shell can be very bright and superficially resembles the disc of a planet, hence the name for this class of object. In some cases, as in this example, the gas expands unevenly and an irregular planetary nebula results. In NGC 6302, some of the gas ejected by the star is travelling outwards at around 400 kilometers per second, indicating a particularly violent outburst. Sco 0.8 13. For details of photographic exposure, search technical table by AAT reference number.