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

→ 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.

The Keplerian orbit that a satellite would follow after a specific time t if all forces other than central inverse-square forces ceased to act from time t on. An osculating orbit is tangent to the real, perturbed, orbit and has the same velocity at the point of tangency.

→ osculating; → orbit.

An orbit whose overall shape is like a parabola; it is the limiting case between an elliptical orbit (eccentricity less than 1) and a hyperbolic orbit (eccentricity larger than 1). The speed necessary to form a parabolic orbit is known as the escape velocity.

→ parabolic; → orbit.

A spacecraft orbit that passes over, or close to, the geographic poles of the Earth or some other solar system object.

→ polar; → orbit.

A satellite that revolves around the Earth in an almost north-south orbit, passing close to both poles. The orbits are sun synchronous, allowing the satellite to cross the equator at the same local time each day. These satellites orbit at a height of 830-880 km and take about 100 minutes to complete a turn around the Earth.

→ polar; → orbit; → satellite.

Same as →prograde motion.

→ prograde motion; → orbit.

An orbit which is in → orbital resonance with another orbit.

→ resonance; → orbit.

An orbit with an inclination between 90° and 270° such as those of some comets and small asteroids orbiting the Sun.

→ retrograde; → orbit.

A → European Space Agency (ESA) mission with strong → National Aeronautics and Space Administration (NASA) participation aimed at studying the Sun up close and from high latitudes, launched on 10 February 2020. Solar Orbiter is equipped with 10 instruments and will provide the first images of the Sun's poles. It will make a close approach of the Sun every six months. Its distance from the Sun varies from within the orbit of → Mercury to close to the orbit of Earth. At closest approach, Solar Orbiter will be about approximately 42 million km from the Sun. Solar Orbiter will combine in situ measurements of the → solar wind around the spacecraft with remote sensing, looking at the Sun's features from afar, to connect the two together. The spacecraft has been tested to withstand temperatures up to 500 °C -- enduring thirteen times the amount of solar heating that satellites in Earth's orbit experience. Solar Orbiter will help us understand how our star creates and controls the → heliosphere, i.e. the giant bubble of → plasma that surrounds the whole → Solar System and influences the planets within it.

→ solar; → orbiter.