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

The fourth brightest star in the sky (V magnitude -0.06) lying in the constellation → Boötes at a distance of about 35 light-years. Arcturus is a red giant of spectral type K2 IIIp.

L. Arcturus, from Gk. Arktouros "guardian of the bear," arktos "bear," → Arctic + ouros "guardian, watcher".

Xersbân "guardian of the bear," from xers "bear" (Mid.Pers. xirs, Av. arša-, cognate with Gk. arktos, Skt. rksa, L. ursus; PIE *rtko-) + -bân suffix meaning "watcher, keeper, guard".
Ar. Semâk-e râmeh.

Put in modern notation, if α and β are acute angles and if β <α, then sin α / sin β <α / β < tan α / tan β. Aristarchus probably used this inequality to show that the Sun is between 18 and 20 times as far from the Earth as the Moon is.

Aristarchus of Samos (c.310-c.230 BC); → inequality.

Same as → archaeoastronomy, megalithic astronomy.

A black amorphous substance produced by heating wood or other natural organic matter in the absence of air. It is used as a fuel.

M.E. charcole, maybe from cherre "char" + cole, → coal.

Zoqâl "live coal, charcoal," variant sokâr; Sogd. askâr; Pashto skor-; Khotanese skara, probably ultimately from Proto-Ir. *uz-gar-, from *uz- "out," → ex-, + *gar "to heat, kindle fire, cook;" cf. Tabari kalə "furnace," kəlen "ash;" Laki koira; Kurd. kulan, kulandan "to cook;" related to garm "warm;" cf. Skt. ghar- "to burn," PIE root *gwher- "to warm, be warm," → warm.

A colorful halo centered on the zenith, appearing when the solar elevation above the horizon is not too high (< 32°).

→ circum-; → zenithal; → arc.

Any extensive record or collection of data, observational (usually obtained with a particular instrument) or theoretical (grid of models usually regarding a particular branch of astrophysics).

→ data; → archive.

A luminous and extremely hot electrical → discharge between two → electrodes when an ionized → plasma is created in the air or gas across the electrodes.

→ electric; → arc.

Of, belonging to, or characteristic of a hierarchy. → hierarchical clustering; → hierarchical cosmology; → hierarchical multiple system; → hierarchical structure formation.

→ hierarchy; → -al.

A model in which a system of self-gravitating particles will gradually aggregate into larger and larger gravitationally bound groups and clusters.

→ hierarchical; → clustering.

A cosmology characterized by clustering of galaxy clusters in increasingly larger systems.

→ hierarchical; → cosmology.

A → multiple star system in which the stars can be divided into two groups, each of which traverses a larger orbit around the system's center of mass. Each of these smaller groups must also be hierarchical, which means that they must be divided into smaller subgroups which themselves are hierarchical, and so on. Hierarchical multiple systems have long-term dynamical stability.

→ hierarchical; → multiple; → system.

A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.

→ hierarchical; → structure; → formation.

A triple star system in which the (inner) binary is orbited by a third body in a much wider orbit. → hierarchical multiple system.

→ hierarchical; → stellar; → system.

A system in which the components are organized in increasingly larger structures.

From O.Fr. ierarchie, from M.L. hierarchia "ranked division of angels," from Gk. hierarchia "rule of a high priest," from hierarches "high priest, leader of sacred rites," from ta hiera "the sacred rites" (neut. pl. of hieros "sacred") + archein "to lead, rule."

Pâygân, from pâyé "step, rank, degree," from pây, pâ "foot, step," from Mid.Pers. pâd, pây; Av. pad- "foot" (cf. Skt. pat; Gk. pos, gen. podos; L. pes, gen. pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-) + -gân suffix forming plural entities, from Mid.Pers. -gânag, -gâna, from Proto-Iranian *kāna-ka-.

A high-precision echelle spectrograph built for exoplanet findings and installed on the ESO's 3.6m telescope at La Silla Observatory in Chile. The first light was achieved in February 2003. HARPS has discovered dozens of exoplanets, making it the most successful planet finder behind the Kepler space observatory. HARPS can detect movements as small as 0.97 m s^-1 (3.5 km h^-1), with an effective precision of the order of 30 cm s^-1, and a → resolving power of 120,000 (Mayor et al., 2003, ESO Messengar 114, 20).

→ high; → accuracy; → radial; → velocity; → planet; → search; → -er.

A → European Space Agency satellite, which was launched in August 1989 and operated until March 1993. It was the first space mission devoted to → astrometry with an unprecedented degree of accuracy. The telescope on Hipparcos had a main mirror of diameter 29 cm. Calculations from observations by the main instrument generated the Hipparcos Catalogue of 118,218 stars charted with the highest precision (published in 1997) containing positions, distances, → parallaxes, and → proper motions. An auxiliary star mapper pinpointed many more stars with lesser but still unprecedented accuracy, in the Tycho Catalogue of 1,058,332 stars. The Tycho 2 Catalogue, completed in 2000, brings the total to 2,539,913 stars, and includes 99% of all stars down to magnitude 11. → Gaia.

Hipparcos, acronym for → High  → Precision  → Parallax  → Collecting → Satellite, chosen for its similarity to the name of the Greek astronomer Hipparchus of Nicaea (c. 190-125 BC), one of the most influential astronomers of antiquity, who compiled an extensive star catalogue in which he gave the positions of over 1,000 stars and also classified them according to their magnitude (on a scale of 1 to 6, brightest to faintest). Ptolemy later incorporated this information into his → Almagest. In addition, he discovered the → precession of the equinoxes.

A → NASA funded project to support and provide to the astronomical community a variety of astronomical data archives, with the primary focus on scientifically related data sets in the optical, ultraviolet, and near-infrared parts of the spectrum. MAST is a huge database that contains astronomical observations of stars, planets and galaxies from 16 separate NASA space science missions, including the Hubble Space Telescope. It is located at the Space Telescope Science Institute (STScI).

In honor of senator Barbara A. Mikulski for her active support for science, NASA, and the astrophysics community; → archive; → space; → telescope.

A unit of angle equal to one thousandth of an → arcsecond, or 1/3 600 000 degree.

→ milli-; → arcsecond.

A → multiple star system that lacks the characteristics of a → hierarchical multiple system.

→ non-; → hierarchical; → multiple; → system.

A large number of narrow filaments in → radio continuum occurring toward the → Galactic Center, about 15 to 20 arc-minutes (some 50 parsecs in projection) north of → Sgr A*. The radio Arc is the prototype of → non-thermal filaments (NTFs) and resolves into a set of more than a dozen vertical filaments with lengths of about 30 pc distributed symmetrically with respect to the → Galactic equator (Yusef-Zadeh et al. 1984, Nature 310, 557). Among more than 100 NTFs found in the Galactic center region, the Arc is the only one known to show inverted spectrum with a → spectral index α = +0.3 (Law et al. 2008, ApJS 177, 515, and references therein). This implies a very hard energy spectrum of particles for a source of → synchrotron radiation.

→ radio; → arc.