An Etymological Dictionary of Astronomy and Astrophysics
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In an imaging system, the dependence of its performance on field angle. In other words, the spatial variability of the → point spread function for off-axis sources.

→ an- + → isoplanatism.

The departure from → isoplanicity.

→ an-; → isoplanicity.

A lens designed so as to minimize both its → spherical aberration and → coma.

→ aplanatism; → lens.

An → optical system that is able to produce an image essentially free from → spherical aberration and → coma. See also the → Abbe sine condition.

→ aplanatism; → system.

Freedom from spherical aberration and coma.

Aplanatism, from aplanatic, from a- "negation prefix" + Gk. plane "wandering," from planasthai "to wander" + -tic adjective-forming suffix.

Nâbirahi, from nâ- "negation prefix" + birah "a devious path; a wanderer, who deviates, errs," + -i noun affix.

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).

→ born; → again; → planetary; → nebula.

A star whose spectrum shows striking similarities to → B[e] stars and is evolving into a → planetary nebula (→ preplanetary nebula).

→ compact; → planetary; → nebula; → B[e] star.

A system of forces acting on a body that all are in the same plane.

→ com- + planar adj. from → plane.

A new category of → astronomical objects in the → solar system introduced in a resolution by the 26th General Assembly of the → International Astronomical Union (IAU) on August 24, 2006. The characterizing properties are as follows: 1) It is in orbit around the Sun; 2) It has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a → hydrostatic equilibrium (nearly round) shape; 3) It has not "cleared the neighbourhood" around its orbit; and 4) It is not a → satellite of a → planet, or other non-stellar body. The property 3 reclassified → Pluto from a planet to a dwarf planet because it has not cleared the neighborhood of its orbit (the → Kuiper Belt). The largest known dwarf planets are: → Eris, → Pluto, → Ceres, → Makemake, and → 2015 RR245.

→ dwarf; → planet.

The plane of Earth's orbit around the Sun.

→ ecliptic, → plane.

A catalog of fields along the → ecliptic observed by the → K2 mission. The catalog is hosted at the → Mikulski Archive for Space Telescopes (MAST).

→ ecliptic; → plane; → input; → catalogue.

An imaginary plane → perpendicular to the → axis of a → sphere dividing the sphere into two congruent parts.

→ equator; → plane.

The plane containing a celestial object's equator.

→ equatorial; → plane.

Same as → extrasolar planet.

→ exo- + → planet.

Of, relating to, or resembling an → exoplanet or exoplanets.

→ exoplanet; → -ary.

A → planetary system consisting of → exoplanets orbiting a star other than Sun.

→ exoplanetary; → system.

The passage of an → exoplanet across the face its star.

→ exoplanetary; → transit.

The part of → astrophysics that searches and studies → extrasolar planets.

→ exoplanet; → -logy.

1) The act or process of explaining.
2) A statement made to clarify something and make it understandable.

Verbal noun of → explain.

A planet which belongs to a star other than → Sun, and therefore does not belong to our → solar system; same as → exoplanet.

→ extrasolar; → planet.