An expanding shell of ionized gas ejected from a red giant star in the late stages of stellar evolution. Despite the name, it has no connection to planets. The glowing gas is illuminated by the hot core of the dying star.
Source: science.nasa.gov
25/12/1998

If our Galaxy were a Christmas tree, planetary nebulae would adorn it like colorful lighted ornaments twinkling on a cosmic scale. Glowing shrouds of gas ejected by red giant stars, planetary nebulae like NGC 6578 (left) and IC 3568 last for a mere 10,000 years or so as swollen stellar giants are transformed into fading, cooling white dwarf stars. Meanwhile ... have a safe, happy holiday season and Best Wishes to all from APOD!