born-again planetary nebula
miq-e sayâreyi-ye bâzzâd
Fr.: nébuleuse planétaire recyclée
A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).
compact planetary nebula B[e] star (cPNB[e])
setâre-ye B[e]-ye miq-e sayyâre-yi-ye hampak
Fr.: étoile de nébuleuse planétaire compacte
Of, relating to, or resembling an → exoplanet or exoplanets.
Fr.: système exoplanétaire
interplanetary coronal mass ejections (ICME)
ešâneš-e andarsayyâreyi-ye jerm az tâj
Fr.: éjection de masse coronale interplanétaire
Fr.: poussière interplanétaire
Particles of dust in the → interplanetary medium. They are left-overs from the beginning of the solar system or from other sources such as sublimating comets. Their existence was first deduced from observations of → zodiacal light.
Fr.: gaz interplanétaire
Electrically charged particles of the solar wind and gas liberated from comets within the solar system.
interplanetary magnetic field
meydân-e meqnâtisi-ye andarsayyârei
Fr.: champ magnétique interstellaire
The magnetic field that is carried along with the solar wind and fills the solar system space. It is wound into a spiral structure by the rotation of the Sun. At the Earth's distance from the Sun, it has a strength of about 5 x 10-5 gauss.
Fr.: matière interplanétaire
Material existing in the space between solar system planets. It includes interplanetary gas and dust.
Fr.: milieu interplanétaire
The material contained in the → solar system in the space through which the planets travel. It consists of the smaller objects such as → asteroids, → comets, → meteorites and also a general pervading → interplanetary dust. Moreover a → plasma of charged particles streaming outward from the Sun in the form of the → solar wind contributes to the interplanetary medium.
Fr.: espace interplanétaire
Same as → interplanetary medium.
Of, pertaining to, or resembling a planet or planets.
Fr.: aberration planétaire
The difference between the true position of a planet and its apparent position, due to the time required for light to travel the distance from the planet to Earth. Correction for planetary aberration is necessary in determining orbits.
Fr.: nébuleuse planétaire
A hot envelope of gas ejected from a central evolved star before becoming a → white dwarf. At the end of the → asymptotic giant phase the pulsating → red giant star is surrounded by an extended shell formed by the material ejected from it. As the evolved star contracts, its → effective temperature rises considerably. When it reaches about 30,000 K, the radiated photons become energetic enough to ionize the atoms in the nebula. The nebula becomes then visible in the optical. It shines essentially in a few → emission lines, produced by cascades during recombination or by collisional excitation with electrons. The central stars of planetary nebulae, → CSPNe, are typically 0.6 to 0.8 solar masses. They have → main sequence masses in the range 1 to 8 solar masses, with an average mass of 2.2 solar masses for a standard → initial mass function. Thus a total of about 1.6 solar masses is in average lost during the → AGB and planetary nebula phases. The life-time of planetary nebulae is relatively short. A typical planetary nebula lasts only a few 10,000 years.
→ planetary; → nebula. The name comes from the fact that these objects appear as planetary disks in a low-resolution telescope. The first planetary nebula, designated NGC 7009 or the → Saturn Nebula, was discovered in 1782 by the German-born English astronomer William Herschel (1738-1822), who described it as "planetary nebula."
fizik-e sayyâregân (#)
Fr.: physique des planètes
The study of the structure, composition, as well as physical and chemical properties of the planets of the solar system, including their atmospheres and their immediate cosmic environment.
Fr.: précession planétaire
The motion of the → ecliptic plane caused by the gravitational influence of the other planets, mainly → Jupiter. The observational effect of planetary precession is similar to that of the → lunisolar precession. But planetary precession causes the → equinoxes to move along the ecliptic in the opposition direction (eastward) from that of luni-solar precession (westward) and at a much slower rate: 0''.12 per year. Same as → precession of ecliptic.
planetary ring system
râžmân-e halqehâ-ye sayyâre-yi
Fr.: système d'anneaux planétaires
→ Interplanetary dust and other small particles organized into thin, flat rings encircling a planet. The most spectacular planetary rings known are those around → Saturn, but the other three → giant planets of the solar system (→ Jupiter, → Uranus, and → Neptune) have their own ring systems.
The branch of astronomy that deals with the science of planets, or planetary systems, and the solar system.
Fr.: système planétaire
A system composed of a star and all the celestial bodies bound to it by gravity, especially planets and their natural satellites.
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.