density of planetary nebulae

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• Planetary nebula luminosity function — (PNLF) is a secondary distance indicator used in astronomy. It makes use of the [O III| [O III] λ5007 forbidden line found in all planetary nebula which are members of the old stellar populations (Population… …   Wikipedia

• Planetary nebula — A planetary nebula is an emission nebula consisting of a glowing shell of gas and plasma formed by certain types of stars when they die. The name originated in the 18th century because of their similarity in appearance to giant planets when… …   Wikipedia

• List of astronomy acronyms — This is a compilation of acronyms commonly used in astronomy. Most of the acronyms are drawn from professional astronomy and are used quite frequently in scientific publications. However, a few of these acronyms are frequently used by the general …   Wikipedia

• nebula — nebular, adj. /neb yeuh leuh/, n., pl. nebulae / lee , luy /, nebulas. 1. Astron. a. Also called diffuse nebula. a cloud of interstellar gas and dust. Cf. dark nebula, emission nebula, reflection nebula …   Universalium

• Milky Way Galaxy — Large spiral galaxy (roughly 150,000 light years in diameter) that contains Earth s solar system. It includes the multitude of stars whose light is seen as the Milky Way, the irregular luminous band that encircles the sky defining the plane of… …   Universalium

• galaxy — /gal euhk see/, n., pl. galaxies. 1. Astron. a. a large system of stars held together by mutual gravitation and isolated from similar systems by vast regions of space. b. (usually cap.) See Milky Way. 2. any large and brilliant or impressive… …   Universalium

• Cat's Eye Nebula — Composite image using optical images from the HST and X ray data from the Chandra X ray Observatory Observation data …   Wikipedia

• History of Solar System formation and evolution hypotheses — Capture theory redirects here. For the solar capture theory, see this article s section on Solar System formation. For the lunar capture theory, see this article s section on lunar formation. Ideas concerning the origin and fate of the world date …   Wikipedia

• Star — For other uses, see Star (disambiguation) …   Wikipedia

• Stellar classification — In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are… …   Wikipedia

• Ring Nebula — For the Ring Nebula in Barnard s Galaxy, see Ring Nebula (NGC 6822). The Ring Nebula M57, The Ring Nebula. Credit: NASA/STScI/AURA …   Wikipedia