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

A meteor shower that appears to emanate from the constellation → Orion. It peaks between October 14 and 20 with about 20 meteors per hour.

→ Orion + → -ides.

1) A child who has lost both parents through death, or, less commonly, one parent.
2) A young animal that has been deserted by or has lost its mother (Dictionary.com). → orphaned protostar.

M.E., from L.L. orphanus "destitute, without parents," from Gk. orphanos "bereaved;" akin to L. orbus "bereaved," Skt. arbhah "weak, child," Armenian orb "orphan," O.Irish orbe "heir," O.C.S. rabu "slave," Ger. Erbe, O.E. ierfa "heir," O.H.G. arabeit, Ger. Arbeit "work," O.E. earfoδ "hardship, suffering, trouble."

Yatim "fatherless," from Ar.

A → protostellar object which has been dynamically ejected from a newborn → multiple star system, either into a tenuously bound orbit or into an escape, thus depriving it from gaining much additional mass. Recent observations have shown that → Class I protostellar sources have a population of distant companions at separations ~ 1000 to 5000 → astronomical unit (AU)s. Moreover, the companion fraction diminishes as the sources evolve. According to N-body simulations of unstable → triple systems embedded in dense cloud cores, many companions are ejected into unbound orbits and quickly escape, but others are ejected with insufficient momentum to climb out of the potential well of the cloud core and associated binary. These loosely bound companions reach distances of many thousands of AU before falling back and eventually being ejected into escapes as the cloud cores gradually disappear (B. Reipurth et al. 2010, arXiv:1010.3307).

→ orphan; → protostar.

A mechanical device that illustrates the relative positions and motions of the planets and moons in the solar system in heliocentric model.

Named after Charles Boyle, 4th Earl of Orrery (1676-1731), for whom the device was first made.

Prefix denoting right, straight, correct.
Prefix indicating that an organic compound contains a benzene ring substituted in the 1.2 position.

Ortho-, from Gk. orthos "set upright, straight, true, correct, regular;" cf. L. arduus "high, steep," O.Ir. ard "high;" also cognate with Av. ərəduua-, as below; from PIE *eredh- "high."

Ardâ-, from Av. ərəduua- "upright, erect, risen;" cf. Skt. ūrdhvá- "upright, tending upward, high;" Gk. ortho, as above.

The → water molecule in which the → nuclear spin of the constituent → hydrogen atoms are → parallel (→ orthohydrogen). In astrophysics the ratio between ortho- and → para-water is used to determine temperatures in → interstellar medium.

→ ortho-; → water.

Of a triangle, the point where the three → altitudes of the → triangle converge.

→ ortho-; → center.

In elementary geometry, pertaining to or involving right angles or perpendiculars.
Of a system of real functions, defined so that the integral of the product of any two different functions is zero.
Of a linear transformation, defined so that the length of a vector under the transformation equals the length of the original vector.
Of a square matrix, defined so that its product with its transpose results in the identity matrix.

→ ortho- + gonia "angle," related to gony "knee;" L. genu "knee;" Mod.Pers. zânu "knee;" Av. žnav-, žnu- "knee;" Skt. janu-; PIE base *g(e)neu-, see below, + → -al

Ardâkonj, from ardâ-, → ortho-, + konj "angle, corner, confined place" (variants xong "corner, angle," Tabari kânj, Kurd. kunj, Hamadâni kom), maybe from the PIE base *g(e)neu-, as above, and related to Mod.Pers. zânu "knee" (Av. žnu-), Skt. kona- "angle, corner," Gk. gony, gonia, L. cuneus "a wedge," Albanian (Gheg dialect) kân "angle, corner," Albanian (Toks) kënd "angle, corner."

A set of functions, any two of which, by analogy to orthogonal vectors, vanish if their product is summed by integration over a specified interval.

→ orthogonal; → function.

Perpendicular lines.

→ orthogonal; → line.

Math.: An → isogonal trajectory where the family of curves are cut at right angles.

→ orthogonal; → trajectory.

Two non-zero vectors which are perpendicular, i.e. their → scalar product is zero.

→ orthogonal; → vector.

1) The property of → orthogonal functions.
2) The following conditions satisfied by the → Fourier series:
∫ cos (mx) sin (nx) dx = 0 (summed from -π to +π) for all m, n
∫ cos (mx) cos (nx) dx = 0 (summed from -π to +π) for all m ≠ n, = 2π for m = n = 0, = π for (m = n) > 0
∫ sin (mx) sin (nx) dx = 0 (summed from -π to +π) for m ≠ n, = π for (m = n) > 0.

→ orthogonal; → -ity.

Molecular hydrogen in which the nuclei (protons) of the two hydrogen atoms contained in the molecule have spins in the same direction. → parahydrogen

→ ortho-; → hydrogen.

Two non-zero vectors that are → orthogonal and have magnitude 1.

→ orthogonal; → vector.

Of or relating to a crystalline structure characterized by three mutually perpendicular axes of different length. → orthorhombic crystal system.

→ ortho-; → rhombic.

A → crystal system that has three mutually perpendicular axes, each of which is of a different length than the others.

→ orthorhombic; → crystal; → system.

Of or relating to an optical system corrected for → distortion.

→ ortho-; → -scopic.

A telescopic eyepiece that produces a wide field of view (between 40° and 50°). The eyepiece consists of a single element lens that is normally plano-convex, and a cemented triplet that is usually symmetrical.

→ orthoscopic; → eyepiece.

To have, produce, or generate oscillations. → vibrate.

From L. oscillatus, p.p. of oscillare "to swing," from oscill(um) "swing" + -ate a suffix forming verbs from L. words.

Navidan "to swing, oscillate," from nâvidan, literally "to swing like a ship," from nâv "ship;" O.Pers./Av. *nāv-, O.Pers. nāviyā- "fleet;" Skt. nau-, nava- "ship, boat;" Gk. naus "ship;" PIE *nau- "boat."