The term 'protoplanetary nebula' may refer to either of the following:

 

• A cloud of gas and dust from which planets are formed around a newborn star, as in the solar nebula.

 

• An early stage in the development of a planetary nebula in which the central star has shed its red giant envelope, exposing its hot core. Ultraviolet light from the core has begun to ionize and make visible the surrounding cloud of gas. Examples include the Calabash Nebula and the Egg Nebula.