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A '''planetary nebula''' is a rare type of [[nebula]] that is smaller and fainter than other types of nebulae such as [[diffuse nebulae]].<ref name=seds>[http://www.messier.seds.org/planetar.html Planetary nebulae] from messier.seds.org</ref> They are typically composed of a [[white dwarf]] surrounded by shells of expanding luminous gas.<ref name=britannica>[https://www.britannica.com/topic/planetary-nebula Planetary nebulae] from britannica.com</ref> There are thought to be 20,000 such objects in the [[Milky Way]], though the effects of [[dust]] mean only around 1,800 have been observed.<ref name=britannica/> A superb example of a planetary nebula is the [[Ring nebula]].

A '''planetary nebula''' is a rare type of [[nebula]] that is smaller and fainter than other types of nebulae such as [[diffuse nebulae]].<ref name=seds>[http://www.messier.seds.org/planetar.html Planetary nebulae] from messier.seds.org</ref> They are typically composed of a [[white dwarf]] surrounded by shells of expanding luminous gas.<ref name=britannica>[https://www.britannica.com/topic/planetary-nebula Planetary nebulae] from britannica.com</ref> There are thought to be 20,000 such objects in the [[Milky Way]], though the effects of [[dust]] mean only around 1,800 have been observed.<ref name=britannica/> Superb examples of a planetary nebulae include the [[Ring nebula]], the [[Helix nebula]] and the [[Cat's eye nebula]].

==History==

==History==