An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 27 Search : planetary
planetary transit
  گذر ِ سیاره‌ای   
gozar-e sayyâre-yi (#)

Fr.: transit planétaire   

The passage of an → inferior planet against the disk of the Sun, as viewed from Earth. Mercury and Venus pass in front of the Sun only when they are close to one of their → orbital nodes, at → inferior conjunction. For Mercury this occurs at the beginning of November (the → ascending node) or at the beginning of May (the → descending node), while for Venus it takes place at the beginning of December (the ascending node) or at the beginning of June (the descending node). See also → transit of Mercury, → transit of Venus.

planetary; → transit.

PLAnetary Transits and Oscillations of stars (PLATO)
  پلاتو   
PLATO

Fr.: PLATO   

A space observatory under development by the → European Space Agency for launch around 2024. Its objective is to detect and characterize → exoplanets by means of their → transit signature in front of a very large sample of → bright stars, and measure the seismic oscillations (→ asteroseismology) of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems.

planetary; → transit; → oscillation; → star.

post-planetary nebula star
  ستاره‌ی ِ پسا-میغ ِ سیاره‌ای   
setâre-ye pasâ-miq-e sayyâre-yi

Fr.: étoile post-nébuleuse planétaire   

An evolved star whose → planetary nebula has dissipated.

post-; → planetary; → nebula; → star.

preplanetary nebula (PPN)
  پیش-میغ ِ سیاره‌ای   
piš-miq-e sayyâre-yi

Fr.: pré-nebuleuse planétaire   

A short-lived transition object between the → asymptotic giant branch (AGB) and → planetary nebula phases. See also → post-asymptotic giant branch star (post-AGB).

pre-; → planetary; → nebula. The more commonly used term, → protoplanetary nebula, is a misnomer and must be avoided. Indeed → protoplanetary is widely used to refer to disks around → pre-main sequence stars. Since the term → protoplanet is used to denote planets undergoing formation, the use of the term "protoplanetary nebula" to mean a completely different kind of object is an unfortunate choice (Sahai et al. 2005, ApJ 620, 948).

protoplanetary
  پوروا-سیاره‌ای   
purvâ-sayyâre-yi

Fr.: protoplanétaire   

Of or relating to a → protoplanet or protoplanets.

protoplanet; → -ary.

protoplanetary disk
  گرده‌ی ِ پوروا-سیاره‌ای   
gerde-ye purvâ-sayyâreyi

Fr.: disque protoplanétaire   

A → circumstellar disk of gas and dust surrounding a → pre-main sequence star from which planetary systems form. Protoplanetary disks are remnants of → accretion disks which bring forth stars. Typically, their sizes are ~100-500 AU, masses ~10-2 solar masses, lifetimes ~106-107 years, and accretion rates ~10-7-10-8 solar masses per year. According to the standard theory of planet formation, called core accretion, planets come into being by the growth of → dust grains which stick together and produce ever larger bodies, known as → planetesimals. The agglomeration of these planetesimals of 100 to 1000 km in size into rocky Earth-mass planets is the main outcome of this theory. Beyond the → snow line in the disk, if the masses of these cores of rock and ice grow higher than 10 times that of Earth in less than a few million years, gas can rapidly accrete and give rise to giant gaseous planets similar to → Jupiter. If core building goes on too slowly, the disk gas dissipates before the formation of → giant planets can start. Finally the left-over planetesimals that could not agglomerate into rocky planets or core of giant planets remain as a → debris disk around the central object that has become a → main sequence star. An alternative to core accretion theory is formation of planets in a massive protoplanetary disk by → gravitational instabilities. The validity of these two theories is presently debated. See also → protoplanet.

protoplanet; → disk.

protoplanetary nebula
  پیش-میغ ِ سیاره‌ای   
piš-miq-e sayyâre-yi

Fr.: pré-nebuleuse planétaire   

preplanetary nebula.

proto-; → planetary; → nebula.

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