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

The forces of jets from a comet's nucleus that can cause a rocket-like effect and alter a comet's direction of motion slightly.

→ non-; → gravitational; → force.

A combining form meaning "angled, angular," used in the formation of compound words. → heptagon, → hexagon, → polygon.

From Gk. gonia "angle," related to gony "knee;" L. genu "knee;" Mod.Pers. zânu "knee;" Av. žnav-, žnu- "knee;" Skt. janu-; PIE base *g(e)neu-.

From bar "side; breadth; breast," variant var (Mid.Pers. var "breast;" Av. vouru "wide, broad, extended" (vourucašāni- "looking far"), related to varah- "breast;" cf. Skt. urú- "wide, broad," úras- "breast;" Gk. eurus "wide, broad;" PIE base uer-, ueru-s"wide, broad"); -guš "corner, angle," Mid.Pers. gošak "corner."

A combining form meaning "face" used in the names of geometrical solid figures having the form or number of faces specified by the initial element.

N.L., from Gk -edron, from hedra "seat, base, chair, face of a geometric solid," from PIE root *sed- "to → sit."

Dimé, from dim, → face.

1) Suffix used in the names of subatomic particles (electron, proton, neutron, gluon, etc.), quanta (photon, graviton, etc.), and other minimal entities or components.
2) Suffix used in the meaning of inert gases (e.g. neon, krypton).

1) Probably extracted from → ion.
2) From Gk. -on, neuter of -os adj. ending.

A suffix used to form abstract nouns from verbs to express action, state, or associated meanings.

From L. -tionem, accusative of noun suffix -tio (genitive -tionis).

-eš, from Mid.Pers. -išn.

A suffix used principally in the names of various devices and instruments (klystron; magnetron; cyclotron; synchrotron).

Perhaps a shortening of electron with accidental allusion to the Gk. instrumental suffix -tron, as in arotron "plough;" akin to O.E. -thor, suffix denoting an instrument; L. -trum; Skt. -tra.

A blue star of → apparent visual magnitude 4.96 lying in the → Orion constellation. It has other designations, including: ψ¹ Orionis, BD+01 1005, HR 1789, and HIP 25302. 25 Ori is a → main sequence star of → spectral type B1 V. It lies at a distance of 1,040 → light-years and has a → luminosity of 9,300 MSun, a radius of 5.5 Rsun, and a mass of about 10 Msun. 25 Ori is in fact a → Be star.

A group of nearly 200 low-mass → pre-main-sequence stars, concentrated within ~ 1 of the early → B star  → 25 Orionis, in the component a of the → Orion OB1 Association. The group also harbors the → Herbig Ae/Be star V346 Ori and a dozen other early-type stars. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s^-1, offset ~ 10 km s^-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and 4 km s^-1 from the velocity of widely spread young stars of the Ori OB1a population. This indicates that the 25 Ori group is a distinct kinematic entity. The low-mass members follow a well-defined band in the → color-magnitude diagram, consistent with an age of ~ 7-10 Myr (Briceno et al., 2007, ApJ 661, 1119).

→ 25 Orionis; → group.

An → Apollo asteroid with unusual properties. Phaethon was discovered on October 11, 1983 using the → Infrared Astronomical Satellite. It is dynamically associated with the → Geminid meteor shower. Whereas most established → meteor shower parents are clearly → cometary in nature, the orbit of Phaethon is that of an → asteroid . Its → semi-major axis, → eccentricity, and → orbital inclination are a = 1.271 AU, e = 0.890, and i = 22.2, respectively, and the → Tisserand parameter with respect to → Jupiter is T_J = 4.5 (while the conventional → comets have T_J < 3). The → perihelion distance is remarkably small, q = 0.14 AU. Phaethon is roughly 5 km in diameter. Not to be confounded with → Phaeton.

Named after the Greek myth of Phaethon, son of the Sun god Helios, due to its close approach to our Sun.

A blue star with → apparent visual magnitude 4.59 in → Orion's Sword. Also known as → c Orionis, HD 37018, HR 1892, and HIP 26237. More specifically, it is a → main sequence star of → spectral type B1 V, lying in the → H II region→ NGC 1977. 42 Orionis is approximately 900 → light-years away based on parallax. It is the major source for ionizing photons in NGC 1977. 42 Ori is a → mutiple star system. The primary star, Aa, of magnitude 6.3 has a → companion companion Ab at a separation of 0.16'', and a more distant companion B of 7.5 magnitude at 1.6'' separation. An irradiated → circumstellar disk near 42 Ori has been detected by Bally et al. (2012) in the → HST image using Hα filter (F658N). They identified a bent → protostellar jet HH1064 from Parenago 2042 (the Spindle) in NGC 1977 with numerous → bow shock features. They argue that the arc feature in the Hα Spindle is centered on the star and its brightened side of the arc is facing toward 42 Ori, suggesting that it may be a → proplyd (Kim et al., 2016, arXiv::1606.08271).

Number 42 in → Flamsteed designation; Orionis, genitive of → Orion.

In physics and chemistry, a calculation that relies on basic and established laws without additional assumptions or special models. Experimental input in ab initio calculations is limited to the determination of values of fundamental physical constants.

→ ab initio; → calculation.

1) To leave completely and finally; forsake utterly; desert.
2) To give up; discontinue; withdraw from (Dictionary.com).

M.E. abando(u)nen, from M.Fr. abandoner, from O.Fr. abandoner from adverbial phrase à bandon "at will, at discretion," from à "at, to," → ad-, + bandon "power, jurisdiction," from L. bannum "proclamation."

Râcidan, related to Pers. parhêz, parhiz "to keep away from, abstain, avoid," gurêz, goriz "to flee, run away;" Av. raēc- "to leave, let;" → heritage.

In → geometric optics, a condition for eliminating → spherical aberration and → coma in an → optical system. It is expressed by the relationship: sin u'/U' = sin u/U, where u and U are the angles, relative to the → optical axis, of any two rays as they leave the object, and u' and U' are the angles of the same rays where they reach the image plane. A system which satisfies the sine condition is called → aplanatic.

Named after Ernst Karl Abbe (1840-1905), a German physicist; → sine; → condition.

1) An imperfection in the imaging properties of a → lens or → mirror. The main aberrations are → chromatic aberration, → spherical aberration, → coma, → astigmatism, → distortion, and → field curvature.
2) → aberration of starlight.
See also: → aberration angle→ aberration constan→ aberration of starlight→ aberration orbit→ annual aberration→ chromatic aberration→ constant of aberration→ diurnal aberration→ optical aberration→ planetary aberration→ relativistic aberration→ secular aberration→ spherical aberration→ stellar aberration.

Aberration, from L. aberrationem, from aberrare "go astray," → aberrate.

Birâheš, from birâidan, → aberrate.

The angle tilt required by the → stellar aberration phenomenon in order that a moving telescope points directly to a star.

→ aberration; → angle.

Same as → constant of aberration.

→ aberration; → constant.

→ aberration of starlight

→ aberration; → light.

An apparent displacement in the observed position of a star. It is a result of the finite speed of light combined with the relative motion of the Earth through space. Suppose that you walk through a vertically falling rain with an umbrella over your head. The faster you walk, the further you must lower the umbrella in front of yourself to prevent the rain from striking your face. For starlight to enter a telescope, a similar phenomenon must occur, because the Earth is in motion. The telescope must be tilted in the direction of motion by an angle: tan θ =(v/c), where v the Earth velocity and c the speed of light. The aberration of starlight was discovered by the English astronomer James Bradley (1693-1762) in 1729 by observing → Gamma Draconis. The tilt angle is θ = 20''.50, from which the Earth's orbital speed, 29.80 km s^-1, can be deduced, using the above equation. See also → annual aberration; → diurnal aberration; → secular aberration. → Special relativity modifies the classical formula for aberration, predicting results which differ substantially from those of classical physics for objects moving at a substantial fraction of the speed of light; → relativistic aberration.

→ aberration; → star; → light.

The apparent path described by a star on the → celestial sphere due → annual aberration. A star at the → ecliptic pole is seen to move around a circle of angular radius about 20".50, once a year. A star on the → ecliptic oscillates to and fro along a line of angular half-length 20".50. At an intermediate → celestial latitude, β, the aberration orbit is an ellipse, with semi-major axis 20".50 and semi-minor axis (20".50) sin β.

→ aberration; → orbit.

Of or pertaining to → aberration.

→ aberration; → -al.