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celestial sphere
[astronomy] An imaginary sphere of indefinitely large radius, which is described about an assumed center, and upon which positions of celestial bodies are projected along radii passing through the bodies.
Pronunciation: s ′les·chl ′sfir
radiant
[astronomy] A point on the celestial sphere through which pass the backward extensions of the trail of a meteor as observed at various locations, or the backward extensions of trails of a number of meteors traveling parallel to each other.
A point on the celestial sphere toward which the stars in a moving cluster appear to travel.
[physics] Pertaining to motion of particles or radiation along radii from a common point or a small region.
A point, region, substance, or entity from which particles or radiations are emitted.
Pronunciation: ′rād·ē·nt
altitude curve
[engineering] The arc of a vertical circle between the horizon and a point on the celestial sphere, measured upward from the horizon.
[navigation] A graphical representation of the altitude of a celestial body as it would appear from a single assumed position or a series of assumed positions over a period of time; such curves are precomputed.
Pronunciation: ′al·t′tüd ′krv
angle of vertical
[astronomy] The angle on the celestial sphere between a given vertical circle and the prime vertical circle.
Pronunciation: ′aŋ·gl v ′vrd··kl
antisolar point
[astronomy] The point on the celestial sphere which lies directly opposite the sun from the observer, that is, on the line from the sun through the observer.
Pronunciation: ¦an·tē¦sō·lr ′p⊙int
apparent position
[astronomy] The position on the celestial sphere at which a heavenly body (or a space vehicle) would be seen from the center of the earth at a particular time. Also known as apparent place.
Pronunciation: ′pa·rnt p′sish·n
appulse
[astronomy] The near approach of one celestial body to another on the celestial sphere, as in occultation or conjunction.
A penumbral eclipse of the moon.
Pronunciation: ′pls
astrometric position
[astronomy] The position of a heavenly body or space vehicle on the celestial sphere corrected for aberration but not for planetary aberration. Also known as astrographic position.
Pronunciation: ¦as·tr¦me·trik p′zish·n
astronomical coordinate system
[astronomy] Any system of spherical coordinates serving to locate astronomical objects on the celestial sphere.
Pronunciation: ′as·tr′näm··kl ′kō′⊙rd··nt ′sis·tm
astronomical triangle
[astronomy] A spherical triangle on the celestial sphere.
Pronunciation: ′as·tr′näm··kl ′trī′aŋ·gl
asymptotic cone of acceptance
[geophysics] The solid angle in the celestial sphere from which particles have to come in order to contribute significantly to the counting rate of a given neutron monitor on the surface of the earth.
Pronunciation: ā′sim′täd·ik ¦kōn v ik′sep·tns
autumnal equinox
[astronomy] The point on the celestial sphere at which the sun's rays at noon are 90° above the horizon at the Equator, or at an angle of 90° with the earth's axis, and neither North nor South Pole is inclined to the sun; occurs in the Northern Hemisphere on approximately September 23 and marks the beginning of autumn. Also known as first point of Libra.
Pronunciation: ⊙′tm·nl ′ē·kw′näks
celestial coordinates
[astronomy] Any set of coordinates, such as zenithal distance, altitude, celestial latitude, celestial longitude, local hour angle, azimuth and declination, used to define a point on the celestial sphere.
Pronunciation: s′les·chl kō′⊙rd·nts
celestial equator
[astronomy] The primary great circle of the celestial sphere in the equatorial system, everywhere 90° from the celestial poles; the intersection of the extended plane of the equator and the celestial sphere. Also known as equinoctial.
Pronunciation: s′les·chl i′kwād·r
celestial globe
[astronomy] A small globe representing the celestial sphere, on which the apparent positions of the stars are located. Also known as star globe.
Pronunciation: s′les·chl ′glōb
celestial horizon
[astronomy] That great circle of the celestial sphere which is formed by the intersection of the celestial sphere and a plane through the center of the earth and is perpendicular to the zenith-nadir line. Also known as rational horizon.
Pronunciation: s′les·chl h′rīz·n
celestial latitude
[astronomy] Angular distance north or south of the ecliptic; the arc of a circle of latitude between the ecliptic and a point on the celestial sphere, measured northward or southward from the ecliptic through 90°, and labeled N or S to indicate the direction of measurement. Also known as ecliptic latitude.
Pronunciation: s′les·chl ′lad·′tüd
celestial longitude
[astronomy] Angular distance east of the vernal equinox, along the ecliptic; the arc of the ecliptic or the angle at the ecliptic pole between the circle of latitude of the vernal equinox and the circle of latitude of a point on the celestial sphere, measured eastward from the circle of latitude of the vernal equinox, through 360°. Also known as ecliptic longitude.
Pronunciation: s′les·chl ′län·j′tüd
celestial meridian
[astronomy] A great circle on the celestial sphere, passing through the two celestial poles and the observer's zenith.
Pronunciation: s′les·chl m′rid·ē·n
celestial pole
[astronomy] Either of the two points of intersection of the celestial sphere and the extended axis of the earth, labeled N or S to indicate the north celestial pole or the south celestial pole.
Pronunciation: s′les·chl ′pōl
circle of latitude
[astronomy] A great circle of the celestial sphere passing through the ecliptic poles, and hence perpendicular to the plane of the ecliptic. Also known as parallel of latitude.
[geodesy] A meridian of the terrestrial sphere along which latitude is measured.
Pronunciation: ′sr·kl v ′lad·′tüd
circle of longitude
[astronomy] A circle of the celestial sphere, parallel to the ecliptic.
[geodesy] See: parallel
Pronunciation: ′sr·kl v ′län·j′tüd
circle of perpetual apparition
[astronomy] That circle of the celestial sphere, centered on the polar axis and having a polar distance from the elevated pole approximately equal to the latitude of the observer, within which celestial bodies do not set.
Pronunciation: ′sr·kl v pr′pech··wl ap·′rish·n
circle of perpetual occultation
[astronomy] That circle of the celestial sphere, centered on the polar axis and having a polar distance from the depressed pole approximately equal to the latitude of the observer, within which celestial bodies do not rise.
Pronunciation: ′sr·kl v pr′pech··wl ′äk·l′tā·shn
colure
[astronomy] A great circle of the celestial sphere through the celestial poles and either the equinoxes or solstices, called respectively the equinoctial colure or the solstitial colure.
Pronunciation: k′lʊr
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