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

An imaginary great circle on the sky half-way between the → celestial poles. It is the projection of the → equator of the Earth on the sky.

→ celestial; → equator.

The great circle on the surface of a body formed by the intersection of the surface with the plane passing through the center of the body perpendicular to the axis of rotation. → celestial equator.

From M.L. æquator "equalizer" (of day and night, as when the sun crosses the equator), from æquare "to make equal, equate" + -tor.

Hamugâr, from hamug, → equal + -âr suffix forming agent nous (as in parastâr) or contracted present stem of âvardan "to bring; to cause, to produce."

An imaginary plane → perpendicular to the → axis of a → sphere dividing the sphere into two congruent parts.

→ equator; → plane.

A set of celestial coordinates based on the celestial equator as the primary great circle. The coordinates are → declination and → right ascension.

→ equator; → system.

Of, pertaining to, or near an equator, especially the equator of the Earth.

From → equator + -ial, variant of → -al.

Hamugâri, from hamugâr, → equator, + adj. suffix -i.

The excess of the equatorial diameter over the polar diameter of a celestial object, such as the Earth or the Moon.

→ equatorial; bulge, from O.Fr. bouge "leather bag," from L. bulga "leather bag," of Gaulish origin.

Barâmadegi, from barâmadan "to grow out; to emerge," from bar- "on, upon, up" (Mid.Pers. abar, O.Pers. upariy "above; over, upon, according to," Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + âmadan "to come" (Mid.Pers. âmadan; O.Pers. gam- "to come; to go;" Av. gam- "to come; to go," jamaiti "goes;" cf. Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").

An astronomical → coordinate system for indicating the positions of → celestial objects on the → celestial sphere. The system consists of two components, → right ascension and → declination. Right ascension is the angle between the → vernal equinox and the point where the → hour circle intersects the → celestial equator. The right ascension is always measured eastward from the vernal equinox, in the units of hours, minutes, and seconds. Declination is the angle between the celestial equator and the position of the star measured along the star's hour circle. It is measured in degrees, minutes, and seconds north or south of the celestial equator. By definition, the vernal equinox is located at right ascension 0h and declination 0°. Equatorial coordinates change with time due to the → precession of the Earth's → rotation axis.

→ equatorial; → coordinate; → system.

Celestial coordinates in the → equator system.

→ equatorial, → coordinate.

A telescope mounting consisting of a polar axis pointed toward the celestial pole, and a declination axis supporting the instrument at right angles to the polar axis.

→ equatorial; → mounting.

The plane containing a celestial object's equator.

→ equatorial; → plane.

Of a planet, the distance from the center to the equator. For Earth it is 6,378.1370 km. Jupiter has an equatorial radius 11.2 times Earth's value.

→ equatorial; → radius.

A slow, dense → stellar wind (high → mass loss rate) emanating from equatorial regions of a → B[e] star. The equatorial and → polar winds are the two main wind components in B[e] stars. The mechanism suggested to explain this wind morphology is the rotationally induced → bistability mechanism.

→ equatorial; → wind.

The great circle in the sky defined by the place of the → Galactic plane or the → Milky Way. At an angle of about 62°, the Galactic equator intersects the celestial equator at two points located in the constellations → Monoceros and → Aquila.

→ galactic; → equator.

The plane swept out as the generating ellipse of the → reference ellipsoid rotates about its minor axis.

→ geodetic; → equator.

→ obliquity of the ecliptic.

→ inclination; → Earth; → equator.

The orientation the Earth's equator would have if the nutation was subtracted.

→ mean; → equator.

That component of general precession caused by the combined effect of the Moon, the Sun and the planets on the equatorial protuberance of the Earth, producing a westward motion of the equinoxes along the ecliptic about 50'' per year. According to an IAU resolution adopted in August 2006, the present terminology replaces lunisolar precession.

→ precession; → equator.

Same as → true celestial equator.

→ real; → equator.

The → celestial equator of date, which is the → great circle on the → celestial sphere perpendicular to the instantaneous axis of rotation of the Earth. Its interaction with the → ecliptic defines the → vernal equinox of date and the → autumnal equinox of date.

→ true; → celestial; → equator.

Same as → true celestial equator.

→ true; → equtor.