====== Planetary Nebulae structure ======

A //Planetary Nebula// is a type of 'emission nebula' seen in astronomical observations. They consist of an expanding, glowing shell of ionized gas which was ejected from 'red giant' stars at a late stage in their development.

About 20% of the nebulae are roughly spherical (as might be expected)  but the majority are //not// spherically symmetric - some dramatically so. The mechanisms that produce such a wide variety of shapes and features have not yet been explained.

See: [[https://en.wikipedia.org/wiki/Planetary_nebula|Wikipedia]]

For an example photo, see [[https://www.esa.int/Science_Exploration/Space_Science/Webb/Webb_captures_detailed_beauty_of_Ring_Nebula|M57]](a.k.a. NGC 6720) courtesy European Space Agency website.

//NOTE//: The term 'planetary nebula' originally used in the late 1770s, is a misnomer - they are unrelated to planets //or// exoplanets.