APOD: 2020 October 16 - Planetary Nebula Abell 78

Good Red Friday morning, Rallypoint. Today's Astronomy Picture of the Day (APOD) is titled "Planetary Nebula Abell 78.' The term 'planetary nebula' originates from the planet-like round shape of these nebulae observed by astronomers through early telescopes. The first usage may have occurred as early as January 1779 when French astronomer Antoine Darquier de Pellepoix described in his observations of the Ring Nebula (M57 or NGC 6720): "very dim but perfectly outlined; it is as large as Jupiter and resembles a fading planet."

Planetary nebula Abell 78 shines by the characteristic emission of ionized atoms in the shroud of material shrugged off the central star. The atoms are ionized (they lose electrons) by the star's ultraviolet light. The visible blue-green glow from the nebula's central region is produced from doubly ionized oxygen atoms. The surrounding red emission is from ionized hydrogen. Some 5,000 light-years distant toward the constellation Cygnus, Abell 78 is about three light-years across.

As a star produces elements throughout its life, planetary nebulae likely play a crucial role in the chemical evolution of the Milky Way by expelling these elements into the interstellar medium. Hubble Space Telescope images have revealed that many planetary nebulae are complex in both shape and content. Observations of these nebulae in more distant galaxies yields useful information about their chemical abundances.