What is Planetary nebula?
[[Image:NGC6543.jpg|thumb|NGC 6543, The [[Cat's Eye nebula]]]] [[File:N1535s.jpg|thumb|NGC 1535, an emission nebula]] A '''planetary nebula''' is a [[emission nebula|nebula]] that is made up of [[gas]] and [[Plasma (physics)|plasma]]. They are made by certain types of [[star]]s later in their life. They look like [[gas giant|planets]] through small [[telescope|optical telescopes]].<ref>[http://hubblesite.org/newscenter/archive/releases/1997/38/background/ Hubble witnesses the final blaze of glory of Sun-like stars] {{Webarchive|url=https://web.archive.org/web/20100401191630/http://hubblesite.org/newscenter/archive/releases/1997/38/background/ |date=2010-04-01 }}, Hubblesite.org, 1997-12-17. Retrieved 2008-08-09</ref> They do not last for long compared to a star, only tens of thousands of years. At the end of a [[average|normal]]-sized star's life, in the [[red giant]] phase, the outside layers of a star are ejected. Because the outside is gone, the star shines brightly and is very hot. The [[ultraviolet]] [[radiation]] given off by the center of the star [[ionization|ionizes]] the gas and plasma that was thrown out from the star. This is what causes a planetary nebula to look like it does. While some planetary nebulae look similar, others have very distinct and unique shapes. Scientists are not sure why planetary nebulae can look so different from one another. Scientists think that [[binary star]]s, [[stellar wind]]s and [[magnetic field]]s might be some of the reasons planetary nebulae can look so varied.<ref>Morris M. 1990. Bipolar asymmetry in the mass outflows of stars in transition. In Mennessier M.O. & Omont, Alain (eds) From Miras to planetary nebulae: which path for stellar evolution? Montpellier, France, September 4–7, 1989. ''IAP astrophysics meeting: Atlantica Séguier Frontières'', pp. 526–30. ISBN 978-2-86332-077-8</ref> In the early 21st century some astronomers began calling them “globular nebulas” to avoid confusing them with the protoplanetary nebulas that make planets. ==Observations== [[Imag