An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

A star belonging to a variety of stars located above the → horizontal branch and blueward of the → red giant branch in the → Hertzsprung-Russell diagram of the → halo population.

→ blue; → halo; → star.

Setâregân plural of setâré, → star, âbi, → blue, hâlé, → halo.

A radio galaxy characterized by an emission "halo" surrounding a more intense "core". About 20% of the known extended radio sources are of the core-halo type.

→ core; → halo; → galaxy.

A vast region surrounding a galaxy where dynamical tracers reveal a large amount of → hidden mass. The halo has considerable mass but relatively low luminosity, suggesting the presence of a lot of → dark matter.

→ dark; → matter; → halo.

A roughly spherical aggregation of → globular clusters, as well as the oldest stars and unseen mass that surrounds the Galaxy.

→ galactic, → halo.

1) Meteo.: Rings or arcs that seem to encircle the sun or moon and are the result of the refraction of light through the ice crystals that make up cirrus clouds.
2) → halo of galaxy.

Halo, from L. (acc.) halo, from Gk. halos "ring of light around the sun or moon."

Hâlé, loanword from Ar.

The → probability distribution of the → number of galaxies that a host → dark matter halo of a given mass contains. HOD is a powerful theoretical frame to populate dark matter halos with luminous galaxies. More specifically, it describes the bias between galaxies and dark matter by specifying (a) the probability P(N|M) that a halo of → virial mass M contains N galaxies of a particular class and (b) the relative spatial and velocity distributions of galaxies and dark matter within halos.

→ halo; → occupation; → distribution.

The diffuse, nearly spherical cloud of stars and → globular cluster s that surrounds a → spiral galaxy.

→ halo; → galaxy.

The → halo of galaxy belonging to our → Milky Way.

→ halo; → galaxy.

Old stars with very low metallicities (→ metallicity) found in the → halo of the Galaxy. Also called → population II star.

→ halo; → population.

A faint, wide ring around → Jupiter that has the shape of a doughnut. It is about 22,800 km wide and about 20,000 km thick. This ring starts at 100,000 km from the center of Jupiter. The outer edge of the Halo merges into the → Main ring.

→ halo; → ring.

A member of a group of five chemical elements having closely related and similar properties. The halogens are: fluorine, chlorine, iodine, bromine, and astatine. They make up Group 17 of the → periodic table and can be found on the left-hand side of the → noble gases.

From Gk. halo- prefix from Gk. hals "salt" + → -gen.

A model of the → Milky Way galaxy in which the → Galactic halo (composed of → gas, → magnetic fields, and → cosmic rays) is assumed to be in → hydrostatic equilibrium. Parker (1966) presented the first study of stability considerations between gas, magnetic fields and cosmic rays in an equilibrium configuration. He found that it is difficult to maintain a stable configuration due to magnetohydrodynamic self-attraction (→ Parker instability). Subsequent works taking into account turbulent motions showed that turbulent pressure can mitigate the influence of Parker instabilities. This enabled new attempts to find conditions under which a stable equilibrium configuration of the Galaxy could exist.

→ hydrostatic; → halo.

Spheroidal distribution of dark matter surrounding a galaxy.

→ massive; → halo.

Same as → lunar halo.

→ Moon; → halo.

A class of molecules that contain at least one → halogen atom bonded to → carbon. Organohalogens are abundant on the Earth where they are mainly produced through industrial and biological processes. They have been proposed as → biomarkers in the search for life on → exoplanets. Simple halogen hydrides have been detected in → interstellar medium sources and in → comets. → Methyl chloride (CH₃Cl), the most abundant organohalogen in the Earth's atmosphere, has both → natural and → synthetic production pathways (Fayolle et al., 2017, Nature Astronomy 1, 703).

From organo-, → organ, + → halogen.