right ascension

﻿
right ascension
Refraction Re*frac"tion (r?*fr?k"sh?n), n. [F. r['e]fraction.] 1. The act of refracting, or the state of being refracted. [1913 Webster]

2. The change in the direction of ray of light, heat, or the like, when it enters obliquely a medium of a different density from that through which it has previously moved. [1913 Webster]

Refraction out of the rarer medium into the denser, is made towards the perpendicular. --Sir I. Newton. [1913 Webster]

3. (Astron.) (a) The change in the direction of a ray of light, and, consequently, in the apparent position of a heavenly body from which it emanates, arising from its passage through the earth's atmosphere; -- hence distinguished as atmospheric refraction, or astronomical refraction. (b) The correction which is to be deducted from the apparent altitude of a heavenly body on account of atmospheric refraction, in order to obtain the true altitude. [1913 Webster]

{Angle of refraction} (Opt.), the angle which a refracted ray makes with the perpendicular to the surface separating the two media traversed by the ray.

{Conical refraction} (Opt.), the refraction of a ray of light into an infinite number of rays, forming a hollow cone. This occurs when a ray of light is passed through crystals of some substances, under certain circumstances. Conical refraction is of two kinds; external conical refraction, in which the ray issues from the crystal in the form of a cone, the vertex of which is at the point of emergence; and internal conical refraction, in which the ray is changed into the form of a cone on entering the crystal, from which it issues in the form of a hollow cylinder. This singular phenomenon was first discovered by Sir W. R. Hamilton by mathematical reasoning alone, unaided by experiment.

{Differential refraction} (Astron.), the change of the apparent place of one object relative to a second object near it, due to refraction; also, the correction required to be made to the observed relative places of the two bodies.

{Double refraction} (Opt.), the refraction of light in two directions, which produces two distinct images. The power of double refraction is possessed by all crystals except those of the isometric system. A uniaxial crystal is said to be optically positive (like quartz), or optically negative (like calcite), or to have positive, or negative, double refraction, according as the optic axis is the axis of least or greatest elasticity for light; a biaxial crystal is similarly designated when the same relation holds for the acute bisectrix.

{Index of refraction}. See under {Index}.

{Refraction circle} (Opt.), an instrument provided with a graduated circle for the measurement of refraction.

{Refraction of latitude}, {longitude}, {declination}, {right ascension}, etc., the change in the apparent latitude, longitude, etc., of a heavenly body, due to the effect of atmospheric refraction.

{Terrestrial refraction}, the change in the apparent altitude of a distant point on or near the earth's surface, as the top of a mountain, arising from the passage of light from it to the eye through atmospheric strata of varying density. [1913 Webster]

The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

• Right ascension — (abbrev. RA; symbol α) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.ExplanationRA is the celestial equivalent of… …   Wikipedia

• Right ascension — Right Right (r[imac]t), a. [OE. right, riht, AS. riht; akin to D. regt, OS. & OHG. reht, G. recht, Dan. ret, Sw. r[ a]tt, Icel. r[ e]ttr, Goth. ra[ i]hts, L. rectus, p. p. of regere to guide, rule; cf. Skr. [.r]ju straight, right. [root]115. Cf.… …   The Collaborative International Dictionary of English

• Right ascension — Ascension As*cen sion, n. [F. ascension, L. ascensio, fr. ascendere. See {Ascend}.] 1. The act of ascending; a rising; ascent. [1913 Webster] 2. Specifically: The visible ascent of our Savior on the fortieth day after his resurrection. ( Acts i.… …   The Collaborative International Dictionary of English

• right ascension — ► NOUN Astronomy ▪ position measured along the celestial equator, expressed in hours, minutes, and seconds …   English terms dictionary

• right ascension — n. Astron. the angular distance of the hour circle of a celestial body from the vernal equinox, measured eastward along the celestial equator and expressed in degrees (from 0 to 360) or, more commonly, in hours (from 0 to 24), minutes, and… …   English World dictionary

• right ascension — Astron. the arc of the celestial equator measured eastward from the vernal equinox to the foot of the great circle passing through the celestial poles and a given point on the celestial sphere, expressed in degrees or hours. [1585 95] * * * ▪… …   Universalium

• right ascension — noun (astronomy) the equatorial coordinate specifying the angle, measured eastward along the celestial equator, from the vernal equinox to the intersection of the hour circle that passes through an object in the sky; usually expressed in hours… …   Useful english dictionary

• right ascension — right′ ascen′sion n. astron. the arc of the celestial equator measured eastward from the vernal equinox to the foot of the great circle passing through the celestial poles and a given point on the celestial sphere, expressed in degrees or hours • …   From formal English to slang

• right ascension — noun Date: 15th century the arc of the celestial equator between the vernal equinox and the point where the hour circle through a given body intersects the equator reckoned eastward commonly in terms of the corresponding interval of sidereal time …   New Collegiate Dictionary

• Right ascension — …   Википедия