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

The mixture of gases of which the earth's atmosphere is composed. It is chiefly made up of Nitrogen (about 78%) and Oxygen (about 20%).

Air, from O.Fr. air, L. aer, Gk. aer, related to Gk. aura "breath, vapor;" PIE *wer- "to raise, lift."

Havâ, from Ar., probably a loanword from Mid.Pers. vây "weather," Av. vayah-, vaya- "weather, atmosphere," from va- "to blow." Cf. Skt. va-, Gk. aemi- "to blow;" Av. vâta- "wind," Skt. vata-, L. ventus, Mod. Pers. bâd "wind." PIE *we- "to blow".

Same as → cosmic-ray shower.

→ air; → shower.

A machine capable of flying by means of → buoyancy or → aerodynamic forces, such as an airplane, helicopter, glider, or balloon.

→ air; → craft.

The faint ever-present glow in the → night time → sky caused by the → collision of → atoms and → molecules in Earth's → upper atmosphere with high energy → particles and → radiation, mainly from the → Sun. The airglow, also called nightglow, varies with time of night, → latitude, and → season.

→ air; → glow; → night.

A measure of the path length traversed by starlight through Earth's atmosphere before it reaches the detector; it is taken relative to the length at the zenith.

→ air; → mass.

The bright disk-like image of a point source of light, such as a star, as seen in an optical system with a circular → aperture.

Named after Sir George Biddell Airy (1801-1892), Astronomer Royal, great administrator, who much improved the equipment at Greenwich Observatory. → disk.

Gerdé, → disk; Airy, see above.

A → transit circle that defines the position of the → Greenwich Meridian since the first observation was taken with it in 1851. Airy's transit circle lies at longitude 0°, by definition, and latitude 51° 28' 38'' N.

Named after Sir George Biddell Airy (1801-1892), Astronomer Royal, at the Royal Observatory in Greenwich from 1835 to 1881. Airy transformed the observatory, installing some of the most advanced astronomical apparatus of his day and expanded both staff numbers and their workload; → transit; → circle.

The fraction of the total light or other radiation which falls on a non-luminous body, such as a → planet, → satellite, or → asteroid, and which is reflected by it. Generally, the albedo is equal to the ratio between the light quantity reflected and the light quantity received. The albedo values range between 0.0 (0%), for a perfectly black area, which absorbs all incident light, and 1.0 (100%) for a perfect reflector. The planets or planetary satellites with dense atmospheres have greater albedos than those of transparent atmospheres or of no atmospheres. The albedo can vary from one surface point to another, so that a mean albedo is given for practical purposes. The natural surfaces reflect different light quantities in different directions and the albedo can be expressed in several ways, depending on the way in which the measurement was made: in one direction or, on the average, in all directions (M.S.: SDE). See also → Bond albedo, → geometric albedo.

Albedo, L. "whiteness," from albus "white," from PIE base *albho- "white". Compare with Gk. alphos "white leprosy," O.H.G. albig, O.E. elfet "swan, the white bird". The idea of whiteness derives from the fact that whiter bodies have a higher reflective power, while opaque objects are more absorptive.

Sepidâ, from sepid, →, white, + -â noun-forming prefix from certain adjectives.

The second brightest star of the constellation → Cygnus, with a visual magnitude of 3.0. It is a double star of strikingly different colors, with components separated by 35''. The brighter component is a K3 giant while its partner is a main-sequence B9 star. About 380 → light-years away, the two rotate around each other with a period of about 75,000 years. The main component is itself a binary system.

Albireo may be a corruption of the L. phrase ab ireo "from the rainbow," as suggested by some writers on star names. It does not mean "the hen's beak".

Menqâr-e Dajâjé "hen's beak," from Ar. Minqâr al-Dajâjah, from minqâr "beak" + dajâjah "hen".
Nok-e Mâkiyân "beak of the hen," from Mod.Pers. nok "beak" + mâkiyân "hen".

An organic compound having a → hydroxyl (-OH) group attached to a carbon atom. Specifically the term is applied to ethyl alcohol or → ethanol (C₂H₅OH). Alcohol exists abundantly in the → interstellar medium in gaseous state also in the form of → methanol.

The discovery of alcohol is attributed to the Iranian physician and scientist Mohammad son of Zakariyâ Râzi (864-930 AD, known in Europe as Razes or Rhazes). He wrote in Ar., which was the scientific language of that period. However, he himself did not use a specific term for this substance as far as we know. Alcohol was first used in medicine about 1250 by two Italian physicians Valis de Furo and Thaddaeus of Florence. It was not yet called alcohol, but aqua ardens or aqua vini. The name alcohol, of Arabic origin, was introduced by the Swiss alchemist and physician Paracelsus (1493-1541) in the sixteenth century. It is composed of two parts, al-, a definite article (like "the"), plus a second component the origin of which is not clear. A broadly spread explanation for the second component is (kuHl) الکحل, originally the name of antimony reduced to a fine powder used especially to darken eyelids. The powder is prepared by sublimation of the natural mineral antimony sulfide (Sb₂S₃). According to this opinion, the meaning of alkuhl would have been first extended by European alchemists to distilled substances in general, and then narrowed to ethanol. Paracelsus indeed defines the terms alcohol and alcool as "the most subtle part of anything." It is in that sense that he calls the substance alcool vini, that is, the most subtle part of wine. Moreover, it is always as "alcool vini" or "alcohol vini" that he uses this term, never "alcohol" alone. Later chemists dropped the "vini" and let the alcohol stand alone for the name (see M. M. Pattison Muir, Story of Alchemy and the Beginning of Chemistry, 1902, p. 192). We note that the word used in current Ar. for this substance is الکحول (alkuHul) and not الکحل (alkuHl). That word may be the Ar. rendering of the European term (probably from the older Fr. form alcohol) loaned in modern times. Alternatively, the word alcohol would originate from another Ar. word, al-ghaul (الغول), meaning "an oppression of the mind, a loss of the senses (from drunkenness), a head-ache" also "spirit, demon." This derivation would be consistent with the use of "spirit" or "spirit of wine" as synonymous of "alcohol" in most Western languages. If this second etymology is correct, the popular etymology and the spelling "alcohol" would not be due to generalization of the meaning of al-kuhl, but rather to Western alchemists and authors confusing the two words al-kuhl and al-ghaul, because of the lack of the "gh" sound in European languages. The problem with this etymology is that no specific word is found in classical Ar. for designating "alcohol."

A 4th magnitude star lying in the constellation → Ursa Major (also called 80 Ursae Majoris) which forms a visual pair with the brighter star → Mizar (Zeta Ursae Majoris). Alcor is separated by about 11.5 minutes of arc from Mizar. It is a → main sequence star of type A5 with a mass of 1.8 Msun. Recent observations show that Alcor is a → spectroscopic binary, whose → companion has M-band (λ = 4.8 μm) magnitude 8.8 and projected separation 1''.11 (28 AU) from Alcor. The companion is most likely a low-mass (~ 0.3 Msun) active star which is responsible for Alcor's → X-ray emission detected by → ROSAT (L_X ~ 10^28.3 erg/s). Alcor is a nuclear member of the → Ursa Major star cluster (distance ~ 25 pc, age ~ 0.5 Gyr). The Alcor binary is probably → gravitationally bound to the Mizar star system, making them a → sextuplet with physical separation 0.36 pc, or 74,000 → astronomical units (Mamajek et al., 2010, AJ 139, 919).

Alcor, perhaps from Ar. al-khawr "the low ground."

Sohâ, from Ar. Suhâ.

The brightest star in the → Pleiades, located in the constellation → Taurus. → Apparent visual magnitude 2.87, → spectral type B7 III.

In Gk. mythology, a daughter of Aelous who, with her husband, Ceyx, was transformed into a kingfisher.

Nayyer-e Sorayyâ "the bight of the Pleiades," from Ar. nayyir "luminous" + Thorayyâ "the Pleiades".
Raxšân-e Parvin "the bight of the Pleiades," from Mod.Pers. raxšân "bright, luminous" + Parvin "the Pleiades".

The brightest star in the constellation → Taurus (visual magnitude about 0.9), Aldebaran is an orange K-type giant that lies 60 → light-years away. It has a faint M2 V companion. It is slowly and irregularly variable.

Ar. Aldebaran "the follower" (of the Pleiades, which rise shortly before it does), from al "the" + dabaran "follower," from dobur "to follow". Gâvcašm "the bull's eye," from Mod.Pers. Gâv "bull, cow" + cašm "eye," corresponding to the alternative Ar. name of the star Ayno 's Sowr.

Any of a class of organic compounds containing the -CH=O group, that is a double-bonded oxygen and hydrogen bonded to the same terminal carbon atom.

From N.L. al(cohol) dehyd(rogenatum) "alcohol deprived of hydrogen."

The brightest star in → Cepheus and a → subgiant star of apparent visual magnitude 2.44. Its → spectral type is A7 and distance 49 → light-years.

Alderamin, from Ar. al dhirâ' al-yamin "right arm" (of Cepheus), from Ar. dhirâ' "arm" + yamin "right".

Zerâ'-e Yamin, from Ar. al dhira al-yamin.

1) The first letter of the Hebrew alphabet (ℵ).
2) A → cardinal number representing an uncountable set. For example, ℵ₀ (pronounced aleph-null, aleph-nought, or aleph-zero) is the smallest infinite cardinal and ℵ₁ is the smallest cadinal larger than ℵ₀.

Hebrew and Phoenician letter, from Semitic languages.

A dark space or band between the primary and secondary rainbows when both are visible. This effect is due to the minimum refraction angle for the → primary rainbow and the maximum for the → secondary rainbow. The only light in the dark region is caused by (a small amount of) scattering, and not the refraction of light in water droplets.

Named for Alexander of Aphrodisias, Greek Peripatetic philosopher and commentator, who first described the effect in 200 AD.

A set of tables created in Toledo, under Alfonso X, el sabio, king of Castile and Léon (1252 to 1284) to correct the anomalies in the → Toledan Tables. The starting point of the Alfonsine Tables is January 1, 1252, the year of king's coronation (1 June). The original Spanish version of the tables is lost, but a set of canons (introductory instructions) for planetary tables are extant. They are written by Isaac ben Sid and Judah ben Moses ha-Cohen, two of the most active collaborators of Alfonso X. The Alfonsine Tables were the most widely used astronomical tables in the Middle Ages and had an enormous impact on the development of European astronomy from the 13th to 16th century. They were replaced by Erasmus Reinhold's → Prutenic Tables, based on Copernican models, that were first published in 1551.The Latin version of the Alfonsine Tables first appeared in Paris around 1320, where a revision was undertaken by John of Lignères and John of Murs, accompanied by a number of canons for their use written by John of Saxony. There is a controversy as to the exact relationship of these tables with the work commissioned by the Spanish king.

After the Spanish monarch Alfonso X (1221-1284); → table.

The ratio of the flow velocity to the → Alfvén speed in a medium.

→ Alfvén wave; → number.

1) In theories of magnetized → accretion disks, the distance from a non-rotating star where the → free fall of a spherical accretion flow is stopped, which occurs where the → ram pressure of the infalling matter equals the → magnetic pressure of the star.
2) The distance from an accreting or wind-blowing star where the → Alfvén Mach number of the flow (→ inflow or → outflow) is unity.

→ Alfvén wave; → radius.