An Etymological Dictionary of Astronomy and Astrophysics
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Theoretical prediction according to which a → giant planet, formed in the outer regions of a → protoplanetary disk, could migrate inward by losing → energy and → angular momentum as the result of → gravitational interactions with the remnants of the disk. This orbital migration could explain the presence of giant gaseous Jupiter-like planets (→ hot Jupiters) very close to their host stars.

→ orbital; → migration.

One of the two points of intersection of the orbit of a secondary body with the plane of reference through the primary.

→ orbital; → node.

→ orbital element.

→ orbital; → parameter.

The time interval between two successive passages of an object through the same point in its orbit around another object.

→ orbital; → period .

In → photometry of → binary stars or → two-body systems, the number of whole or fractional orbits completed, from the point the photometry begins. The point is conventionally chosen as the position at which the → primary star eclipses the → secondary star, and therefore the → light curve is at a minimum. The phase keeps counting indefinitely, thus the secondary star gets eclipsed at phase 0, 1, 2, 3, and so on. At these phases the primary lies between the secondary and the observer. An orbital phase of 0.5 corresponds to halfway through the binary orbit, 0.75 is three-quarters the way through, and so on.

→ orbital; → phase.

The photometric variability induced by the → orbital motion in a → two-body system.

→ orbital; → phase.

The plane defined by the motion of an object about a primary body.

→ orbital; → plane .

Same as → relativistic precession.

→ orbital; → precession.

The situation in which two orbiting objects exert a regular, periodic gravitational influence on each other and therefore their orbital frequencies are related by a ratio of two small → integers. Orbital resonance often results in an unstable interaction in which bodies exchange momentum and shift orbits until the resonance disappears. The resonance increases the eccentricity until a body approaches a planet too closely and the body is slung away.

→ orbital; → resonance.

The lessening in size of the orbit of a binary system composed of two compact objects (pulsars/black holes) due to loss of energy by the system, in particular through gravitational wave radiation. This loss will cause the two objects to approach closer to each other, the orbital period decreases and the binary companions will eventually merge.

→ orbital; shrinkage, from shrink, from M.E. schrinken, O.E. scrincan, from P.Gmc. *skrenkanan (cf. M.Du. schrinken, Swed. skrynka "to shrink."

Darhamkešidegi "shrinking, shriveling," from state noun of < i>darhamkešidé, from darham- "together, in eachother, toward eachother" (For etymology of dar-, → in-; for etymology of ham-, → com-) + kešidé "drawn, shrivelled, wrinkled," from Mod./Mid.Pers. kešidan, kašidan "to draw, protract, trail, drag, carry," dialectal Yaqnavi xaš "to draw," Qomi xaš "streak, stria, mark," Lori kerr "line;" Av. karš- "to draw; to plow," karša- "furrow;" Proto-Iranian *kerš-/*xrah- "to draw, plow;" cf. Skt. kars-, kársati "to pull, drag, plow;" Gk. pelo, pelomai "to move, to bustle;" PIE base k^wels- "to plow;" madâri, → orbital.

Same as → orbital velocity.

→ orbital; → speed.

The velocity of an object in a given orbit around a gravitating mass. For a perfect circular orbit, the velocity is described by the formula V =√[G(M + m)/r], where G is the gravitational constant, M the mass of the primary gravitating body, m the mass of the orbiting object, and r the radius of the orbit.

→ orbital; → velocity.

A → spacecraft or → satellite designed to orbit a planet or other → solar system body.

→ orbit; → -er.

In astronautics, the study of satellite orbits and precise determination of orbital elements which gives the exact position of the satellite.

→ orbital + → -graphy.

1a) General: The way in which several items are arranged, as an indication of their relative importance or size or when each will be dealt with.
1b) Optics: → order of interference.
1c) Math.: The number of rows or columns of a → square matrix or → determinant.
1d) Math.: The highest → derivative appearing in a given → differential equation. For example,
d²y/dx² + 2y (dy/dx) - 3 = 0
is a differential equation of order two.
2) To arrange, regulate, or dispose things in their proper places. See also: → disorder, → first-order differential equation, → first-order partial derivative, → first-order spectrum, → interference order, → order of a tensor, → order of interference, → order of magnitude.

From O.Fr. ordre, from earlier ordene, from L. ordinem (nominative ordo) "row, rank, arrangement."

Râyé, noun related to râyânidan "to regulate, set in order," from Mid.Pers. râyânīdan "to arrange, organize," from rây- (Mod.Pers. ârây-, ârâyeš, ârâyidan "to arrange, adorn"), ârây-, ârâstan "to arrange, adorn;" O.Pers. rād- "to prepare," rās- "to be right, straight, true," rāsta- "straight, true" (Mod.Pers. râst "straight, true"); Av. rāz- "to direct, put in line, set," razan- "order;" Gk. oregein "to stretch out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" Skt. rji- "to make straight or right, arrange, decorate;" PIE base *reg- "move in a straight line;" see also → direct.

The → number of → vertices.

→ order; → graph.

The maximum number of the indices (→ index) of a tensor.

→ order; → tensor.

A whole number which characterizes a particular position of an interference fringe according to whether there is interference arising from one, two, three, etc. wavelength difference of path. Same as → interference order

→ order; → interference.

Value of a number or of a physical quantity given roughly, usually expressed as a power of 10. Thus, 2.5 x 10⁵ and 6.4 x 10⁵ are of the same order of magnitude, and 2 x 10⁷ is 2 orders of magnitude greater than either.

→ order; → magnitude.

Characterized by → order; arranged according to a rule. → ordered tree.

→ order + -ed.