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

1) The act or process of calibrating or the state of being calibrated.
2) A set of graduations that show positions or values.

Calibration, noun from → calibrate.

Kabizeš, noun from kabizidan, → calibrate.

An empirical curve obtained through appropriate exposures in order to determine the instrument's response. For example, a curve allowing the conversion of relative intensities of an observed object into absolute fluxes, or a curve relating the detector's pixel positions to wavelengths.

→ calibration; → curve.

A systematic error in the constant values to be applied to a measuring instrument.

→ calibration; → error.

Irang, → error; kabizeš, → calibration.

An exposure obtained with an instrument mounted on the telescope using an artificial illuminating source in order to calibrate the instrument.

→ calibration; → exposure.

Nurdâd, → exposure; kabizeš, → calibration.

A lamp used for instrument calibration, such as an internal He-Ar arc for wavelength calibration or an external source of light placed in the telescope dome for flat-field exposures.

→ calibration; lamp, from O.Fr. lampe, L. lampas, from Gk. lampas "torch, lamp, light, meteor," from lampein "to shine."

Kabizeš, → calibration; lâmp, from Fr., as above.

Daily geometrical libration of the Moon arising from the fact that observers at different points on the Earth see the Moon from slightly different angles. As the Moon rises in the east, you are positioned on one side of our planet, and by the time it sets in the west. Earth's rotation has carried you to the other side. This change in position produces a slight → parallax effect that adds about another 1° of libration in longitude. Two other geometrical libration are → libration in longitude and → libration in latitude. See also → physical libration.

→ diurnal; → libration.

The → calibration of the flux received by a detector in terms of absolute units.

→ flux; → calibration.

Libration resulting from changes in the location of the observer with respect to body. More specifically, a lunar libration motion that results from the Earth based observer seeing the Moon from different directions at different times. There are three types of geometrical libration: → libration in longitude, → libration in latitude, and → diurnal libration. See also → physical libration.

→ geometric; → libration.

A wavelength calibration of astronomical spectra using a helium-argon light source.

→ helium; → argon; → calibration.

Small oscillations of a → celestial body about its mean position. The term is used mainly to mean the Moon's libration caused by the apparent wobble of the Moon as it orbits the Earth. The Moon always keeps the same side toward the Earth, but due to libration, 59% of the Moon's surface can be seen over a period of time. This results from three kinds of libration working in combination: → libration in longitude, → libration in latitude, and → diurnal libration. See also: → geometrical libration, → physical libration.

L. libration- "a balancing."

Halâzân "to and fro motion, oscillation," literally "a swing: a seat suspended by ropes on which a person may sit for swinging," from Gilaki halâcin "a swing," Ilâmi harazân "a swing," variants (Dehxodâ) holucin, holu "a swing," probably from Proto-Ir. *harz- "to send, to set."
Roxgard, literally "turning the face," from rox, variant ru(y) "face, surface; aspect; appearance" (Mid.Pers. rôy, rôdh "face;" Av. raoδa- "growth," in plural form "appearance," from raod- "to grow, sprout, shoot;" cf. Skt. róha- "rising, height") + gard "turning, changing," from gardidan "to turn, to change" (Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- "to turn, bend").

A tiny oscillating motion of the Moon arising from the fact that the Moon's axis is slightly inclined relative to the Earth's. More specifically, the Moon's polar axis is tilted nearly 7° with respect to the plane of its orbit around Earth. Hence for half of each orbit we see slightly more of the north pole when its tipped toward us, and for the other half we see slightly more of its south pole. Libration in latitude displaces the mean center of the Moon north-south by between 6°.5 and 6°.9.

→ libration; → latitude.

A tiny oscillating motion of the → Moon arising from the fact that the Moon's orbit is not a precise circle but rather an → ellipse. Therefore, Moon is sometimes a little closer to the Earth than at other times, and as a result its → orbital velocity varies a bit. Since the Moon's rotation on its own axis is more regular, the difference appears as a slight east-west oscillation. Libration in longitude is the most significant kind of libration. It varies between about 4°.5 and 8°.1 because of gravitational perturbations in the Moon's orbit caused by the Sun.

→ libration; → longitude.

A calibration which converts the measured relative magnitudes into an absolute photometry.

→ photometric + → calibration.

A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon's rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon's near side. The Moon's physical libration is about 0.03° in longitude and about 0.04° in latitude.

→ physical; → libration.