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

A coordinate in the → equatorial system measured from the → vernal equinox eastward to the point where the object → hour circle intersects the → celestial equator. Right ascension (symbol α) is expressed in hours, minutes, and seconds. See also: → declination.

→ right; ascension, M.E. ascencioun, from O.Fr., from L. ascendere "to climb up," from → ad- "to" + scandere "to climb."

Râst, → right; afrâz present stem of afrâzidan, afrâštan "to raise, exalt, extole," from Mid.Pers. abrâstan, abrâz- "to lift, raise," from ab-, from O.Pers./Av. abiy-/aiwi- "to, upon, against;" cf. Skt. abhi-, Gk. amphi- + râst "straight, direct, true;" from O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Ger. recht; E. right; PIE base *reg- "move in a straight line," hence, "to direct, rule."

A triangle one of whose angles is a → right angle.

→ right; → triangle.

See → Fleming's rules.

→ right; → hand; → rule.

A rule that gives the direction of the resultant vector in a → vector product: A x B = C. It is the direction of advance of a right-hand screw whose axis, held perpendicular to the plane of A and B, is rotated in the same sense that rotates the first-named vector (A) into the second-named vector B through the smaller angle.

→ right; → hand; → screw; → rule.

Using the right hand with greater skill or ease than the left.

→ right; → hand + -ed.

Râstâl, from râst, → right, + -al→ -al. Râstdast, with dast, → hand.

1) General: Stiff or unyielding; inflexible, strict, severe.
2) Physics: → rigid body; → rigidity.

From L. rigidus "hard, stiff, rough," from rigere "to be stiff;" related to L. frigus "cold," Gk. rhigos "frost, cold."

Saxtpây, from saxt, → hard, + pây present stem of pâyidan "to stand firm, to be constant, steady, fixed;" Mid.Pers. pâyitan, pâtan, pây- "to protect; wait, stand," Sogdian p'y "to protect, watch over;" O.Pers./Av. pâ(y)- "to protect, keep" pâtar- "protector, watcher," cf. Skt. pâ- "to protect, keep," pâti "protects;" Gk. poimen "shepherd," poma "lid, cover;" L. pastor "shepherd," panis "bread;" PIE base *pa- "to protect, guard, pasture, feed."

Mechanics: A system of many particles whose positions relative to one another remain fixed.

→ rigid; → body.

1) The quality or state of being → rigid. See also → modulus of rigidity.
2) → magnetic rigidity.

→ rigid + → -ity.

Another name of → Alpha Centauri.

Rigel, from Ar. rijl (رجل) "foot;" Kentaurus, → Centaurus.

Pâ "foot, step" (from Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-); Kentâwros→ Centaurus.

1) Severely exact or accurate; precise.
2) Logic, Math.: Logically valid. See also: → accurate, → exact, → precise.

M.E., from M.L. rigorosus, from rigor "stiffness, rigor," from rigere "to be stiff."

Farsaxt, from far- intensive prefix "much, abundant; elegantly" (Mid.Pers. fra- "forward, before; much; around;" O.Pers. fra- "forward, forth;" Av. frā, fərā-, fra- "forward, forth; excessive;" cf. Skt. prá- "before; forward, in fron;" Gk. pro "before, in front of;" L. pro "on behalf of, in place of, before, for;" PIE *pro-) + saxt "hard, strong, firm, secure, solid, vehement, intense" (Mid.Pers. saxt "hard, strong, severe;" Av. sak- "to understand or know a thing, to mark;" cf. Skt. śakta- "able, strong," śaknoti "he is strong," śiksati "he learns").

A → selection rule obeyed by → discrete transitions. Among them are: rigorous selection rules for → electric dipole transitions (→ permitted) requiring: 1) ΔJ must be 0 or ± 1 with J = 0 ↔ 0 forbidden. 2) ΔM_J = 0, ± 1. 3) → Parity change, i.e. even ↔ odd.

→ rigorous; → selection; → rule.

A long, narrow, straight or sinuous trench or valley with steep walls and roughly parallel sides on the surface of the Moon.

From Ger. Rille "a small rivulet or brook."

Borrowed from E., as above.

The outer edge, border, margin, or brink of something, especially of a circular object.

M.E., from O.E. -rima (in compounds, as in særima "seashore"); cognate with O.Norse rimi "raised strip of land, ridge"

Labé "limb, edge," from lab "lip;" Mid.Pers. lap; cognate with L. labium, E. lip; Ger. Lefze.

A long fissure on the surface of a planet or Moon; plural form rimae.

From L. rima "fissure, slit."

Loan from E., as above.

The coordinates that describe the → Minkowski space-time in a → hyperbolic version of → polar coordinates. If the coordinates in an → inertial frame is denoted by (t,x), the Rindler coordinates (η,ξ) are defined by: t = (1/α) e^αξ sinh (αη) and x = (1/α) e^αξ cosh (αη), where α is some positive constant.

Named after Wolfgang Rindler (1924-), Austrian physicist; → coordinates.

A portion of the → space-time described by → Rindler coordinates.

→ Rindler coordinates; → wedge.

1) A circular band of something. → gossamer ring.
2) A resonant sound like that of a bell or bells.

O.E. hring "circular band" (cf. O.N. hringr, Ger. Ring), literally "something curved," from PIE base *(s)ker- "to turn, bend."

1) Halqé, loan from Ar. Halqat "ring, hoop, circle."
2) Zang "bell."

A galaxy with a ring-like appearance around the central luminous center. The ring consists of massive, relatively young bright stars. It is believed that ring galaxies result from the head-on collision of two different galaxies.

→ ring; → galaxy.

Of → Saturn, the angle measured with respect to the sub-observer point (a line connecting the observer to Saturn) in the direction of the orbital motion.

→ ring; → longitude.

A bright → planetary nebula in the constellation → Lyra, also called M57 or NGC 6720. In small telescopes it has the appearance of a slightly elliptical luminous ring around a central hot star (15th magnitude). The radius is one-third of a → light-year, and the nebula is about 2,000 light-years away.

→ ring; → nebula.