Abbreviation of arc. [(astronomy) That part of a circle which a heavenly body appears to pass through as it moves above and below the horizon.]

(astronomy) Rising at sunset and setting at sunrise, as a star.

alignment; position in a straight line, as of two planets with the sun

A figure-eight curve that results when the Sun's position in the sky is plotted out over the year at the same hour of mean solar time every day. [from 17th c.]

(astrology) Any of the four cardinal points of an astrological chart: the Ascendant, the Midheaven, the Descendant and the Imum Coeli.

(obsolete) A hypothetical Earth on the opposite side of the Sun.

(typography):

(astronomy) That part of a circle which a heavenly body appears to pass through as it moves above and below the horizon.

The parallel of latitude that runs 66° 33′ 39″ north of the Equator, which marks approximately the southernmost place in the Northern Hemisphere where the sun does not set on the summer solstice and does not rise on the winter solstice.

(astrology, of a planet) To have a particular aspect or type of aspect.

autumnal equinox

(astronomy) The moment when the sun appears to cross the celestial equator while tilting away from the observer, taking place in September in the northern hemisphere and March in the southern hemisphere.

(physics, astronomy) The angle between the rotational axis and the orbital axis of an orbiting celestial object.

(astronomy) The axis of Earth between the celestial poles, important in ancient geocentric coordinate systems.

An arc of the horizon intercepted between the meridian of the place and a vertical circle passing through the center of any object.

(astrology) An aspect of two planets that are distant from each other by two fifths of a great circle (72 degrees)

(astronomy) A great circle on the celestial sphere, coincident with the plane of earth's equator.

An imaginary point situated where a planet's axis intersects the celestial sphere.

A treatise consisting of a hundred astrological aphorisms.

(astronomy) About or around the meridian.

(astronomy) Of a celestial body, continually visible above the horizon during the entire 360 degrees of daily travel.

(astrophysics) orbiting around three stars or other centers.

(astronomy) The complement, in spherical coordinates, of a latitude (the difference between a latitude and 90°).

(astronomy) The longitude of the morning terminator (division between illuminated and dark regions) on the Moon, as measured in degrees westward from the prime meridian.

(astronomy) Either of two great circles (meridians) that intersect at the poles and either the equinoxes or solstices.

(astrology) An aspect in which planets are in close proximity to one another.

(astronomy, of multiple planets or other orbiting bodies) Orbiting a central celestial object within the same orbital plane.

(astronomy, geodesy) a clerical convenience in solving systems of linear equations by hand.

(astronomy) The moment when the sun reaches the southernmost point of the sky, occurring on December 21–22. That would be winter solstice in the northern hemisphere and summer solstice in the southern hemisphere.

(obsolete, Ptolemaic astronomy) An imaginary circle surrounding the Earth, in whose periphery either the heavenly body or the centre of the heavenly body's epicycle was supposed to be carried round.

(astronomy) A phase of the moon when it appears half lit and half dark, as at the quadratures.

(astronomy) In the direction of the general planetary motion, or from west to east; in the order of the signs; not retrograde; said of the motion of a celestial body.

(astrology) the path followed by a planet, point, or degree from its rising point to its setting point.

(astronomy) The apparent westward rotation of the celestial sphere, along with the apparent westward revolution of celestial objects, around the celestial poles due to prograde (eastward) rotation of planet Earth relative to the seemingly fixed stars – completed once each sidereal day (about 23 hours, 56 minutes, 4 seconds).

(historical astronomy) The duodecimal divisions of the Chinese seasons, beginning with the second of the three divisions of winter.

The volume of space dominated by Earth's gravity

(astronomy) The eccentricity of the conic section (usually an ellipse) defined by the orbit of a given object around a reference object (such as that of a planet around the sun).

(astronomy) The great circle on the celestial sphere that is the mean apparent path of the sun as viewed from the earth.

(astronomy) The ecliptic, the plane of the Earth's orbit around the Sun, or by extension the orbital planes of other celestial bodies.

Obsolete form of ecliptic. [(astronomy) The great circle on the celestial sphere that is the mean apparent path of the sun as viewed from the earth.]

(astronomy) The angular distance of a planet from the sun

(astronomy) A small circle whose centre is on the circumference of a larger circle; in Ptolemaic astronomy it was seen as the basis of revolution of the "seven planets", given a fixed central Earth.

(obsolete, astronomy) The center of a planetary epicycle.

The celestial equator.

(astronomy) A kind of telescope mounted so as to have two axes of motion at right angles to each other, one of them parallel to the axis of the Earth, and each carrying a graduated circle, one for measuring declination, and the other right ascension, or the hour angle, so that the telescope may be directed, even in the daytime, to any star or other object whose right ascension and declination are known.

(astronomy) The plane that passes through the Earth's equator, or by extension the equators of other celestial bodies.

Rare spelling of equator. [(geography, often “the Equator”) An imaginary great circle around Earth, equidistant from the two poles, and dividing earth's surface into the northern and southern hemisphere.]

Pertaining to the time of equal day and night; applied to the equinoctial line.

A day in which the durations of light and darkness are equal, contrasted with an equinox, where they may differ slightly due to the angular diameter of the sun and atmospheric refraction.

Alternative spelling of equinoctial (of or relating to an equinox). [(astronomy) Of or relating to the spring or autumnal equinox.]

(astronomy) Of or relating to the spring or autumnal equinox.

celestial equator

(astronomy) A meridian on the celestial sphere where the sun crosses it on equinoxes.

(obsolete) celestial equator

The celestial equator.

(astronomy) One of the two points in space where the apparent path of the Sun intersects with the equatorial plane of the Earth.

(obsolete) Alternative form of equinoctial [The great circle midway between the celestial poles; the celestial equator.]

(astronomy) A period of 54 years and 33 days that can be used to predict successive eclipses with similar properties and location.

(historical, geography) A meridian formerly used as a prime meridian; now defined as 18.160792° west.

(astronomy) A point on the celestial sphere where the sun crosses the celestial equator on September equinox.

A coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth, equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth.

(informal) The phenomenon of the Earth revolving around the Sun.

Describing an orbit around the Earth where each passage in the same direction along a given latitude will occur throughout the year at the same true solar time.

(astrology, obsolete) The aspect or position of any two celestial bodies separated by 22.5° (that is, 360° divided by 16) as they appear to an observer on earth.

(astronomy) The great circle through an object whose location is to be determined and the two celestial poles.

(astrology) The point where the ecliptic crosses the northern meridian, said to represent the deep subconscious.

(astrology) A quincunx.

physical material, containing an inscribed message, used as a means of communication between intelligences separated by astronomical distances

(astronomy) The path of such a body

Coming between the equinoxes.

(mathematics, astronomy) The mean plane occupied by the orbit of a satellite during a precession cycle; the plane normal to the orbital precession pole of the satellite.

(astronomy) The angular distance of a heavenly body from the ecliptic.

(by extension) A similar rotational or orbital characteristic of some other celestial body.

(astrophysics) Synonym of Lagrange point

(geography, 'the line' or 'equinoctial line') The equator.

(astronomy) The intersection of an orbiting object's orbital plane with the plane of reference.

(astronomy) The moment when the sun crosses the celestial equator while heading northward, occurring on March 19–21. That would be vernal equinox in the northern hemisphere and autumnal equinox in the southern hemisphere.

In full celestial meridian: a great circle passing through the poles of the celestial sphere and the zenith for a particular point on the Earth's surface.

(astrology) The intersection of the ecliptic and meridian

(by extension) Both the northern and southern hemisphere orbits for the Earth.

The point of the celestial sphere, directly opposite the zenith; inferior pole of the horizon; point of the celestial sphere directly under the place of observation.

(technical) A hole in the gnomon of a sundial, through which passes the ray of light which marks the hour of the day, the parallels of the Sun's declination, his place in the ecliptic, etc.

(astronomy, astrology, obsolete) Synonym of square or quadrature: a rising at a 90 degree angle to the position of another heavenly body, particularly the sun.

(astronomy) The middle to highest point of a part of an ecliptic that is above the horizon at any period of time.

March equinox, when the sun crosses the equator while heading northward.

(astronomy) Any of several irregularities in the precession of the equinoxes caused by varying torque applied to the Earth by the Sun and the Moon.

(astronomy, uncommon) An arc of the equator, which is intercepted between the first point of Aries and that point of the equator which rises together with a star, forming an oblique sphere.

(astronomy, by extension, of a planet) Axial tilt.

(astrology) The aspect of two planets that are 45°, or one-eighth of a circle, apart.

(astrology, rare) The relationship between two planets that are distant from each other by one eighth of a great circle (45.625 degrees)

(astronomy) An octant.

Alternative letter-case form of Omega Point [A maximal level of complexity in the universe, often equated with the Christian God, which some philosophers believe is inevitable.]

(astronomy) The apparent relative position of two celestial bodies when one is at an angle of 180 degrees from the other as seen from the Earth.

(astrology, of planets) joined in aspect by a perfect measure, with no variance

Alternative spelling of pericenter [(astronomy) The peribaryon, the point of closest approach of an astronomical object in an elliptical orbit to its center of attraction.]

(astronomy) A disturbance in the motion of a planet due to its position in its orbit relative to another planet.

(physics, countable) The wobbling motion of the axis of a spinning body when there is an external force acting on the axis.

The slow westward shift of the equinoxes along the plane of the ecliptic, resulting from precession of the earth's axis of rotation, and causing the equinoxes to occur earlier each year

The reference line at 0° longitude, passing through Greenwich, England, from which longitude east and west is measured.

(astronomy) A situation in which the directions of two celestial bodies (or a celestial body and the Sun) form a right-angle from the perspective of the observer.

(astronomy) Dipping towards a center in all directions.

(astrology) An aspect of planets that are distant from each other by one fifth of a zodiac (72°)

(astronomy) An ideal straight line joining the center of an attracting body with that of a body describing an orbit around it, as a line joining the sun and a planet or comet, or a planet and its satellite.

(astronomy) The angular distance east of the vernal point (“the solar zenith at the March equinox”); the celestial equivalent of longitude.

A configuration of wormholes where for each individual wormhole the time difference across its mouths is such that it may not allow a closed timelike curve.

(of an astronomic object) The time taken to rotate about its axis relative to the background stars.

(astrology) An aspect of the planets when distant from each other by half a quadrant, or forty-five degrees, or one sign and a half.

(astrology) An aspect of the planets when distant from each other half of the quintile, or thirty-six degrees.

(astrology) An aspect of the planets when they are distant from each other the twelfth part of a circle, or thirty degrees.

(astrology) An aspect made by two planets when they are 45 degrees apart from each other.

(astronomy) The moment when the sun crosses the celestial equator while heading southward, occurring on September 22–23. That would be autumnal equinox in the northern hemisphere and vernal equinox in the southern hemisphere.

(astrology) Of or noting the aspect or position of any two celestial bodies separated by 135°.

(astronomy) The constellation Sextans.

(astronomy, astrology) Of or denoting the aspect or position of any two celestial bodies separated by 60°.

(astronomy) The rotational period of Earth; the time in which Earth rotates around its axis 360 degrees.

(astronomy) The sidereal day of a planet. (I.e., in the definition for "sidereal day", replace "Earth" by the given planet.)

(astronomy) Time measured by the apparent diurnal motion of the vernal equinox; approximated by that based on the rotation of planet Earth relative to the seemingly fixed stars.

(astronomy) A solar day on the planet Mars (equivalent to 24 hours, 39 minutes, 35 seconds).

Measured by the progress or revolution of the sun in the ecliptic; as, the solar year.

One of the two points in the ecliptic at which the sun is furthest from the celestial equator. This corresponds to one of two days in the year when the day is either longest or shortest.

(astronomy) A meridian on the celestial sphere where the sun crosses it on solstices.

(astronomy) The roughly 1460-year cycle between successive alignments of the first days of the Egyptian civil calendar and the observational Sothic year.

September equinox, when the sun crosses the equator while heading southward.

(astronomy) vernal equinox

(cosmology) In geocentric cosmologies, that region of the cosmos from the centre of the Earth to the moon, believed to comprise the four classical elements (earth, air, fire and water) and to be subject to generation and corruption.

A right line on which the style, or gnomon, of a sundial is erected, being the common section of the face of the dial and a plane perpendicular to it passing through the style.

(astronomy) The moment when the Earth is in that point of its orbit where the northern or southern hemisphere is most inclined toward the sun.

(astronomy) The apparent orbital period of a planet as seen from Earth.

(astronomy, historical) An instrument used to show how the rotation of the Earth on its axis and its orbit around the Sun cause day and night and the seasons.

An aspect of two planets with regard to the Earth when they are distant from each other ninety degrees, or a quarter-circle.

(astronomy) The problem of calculating the motion of three celestial bodies that interact with each other gravitationally

(countable, astrology) A trine; an aspect of two planets distant 120 degrees from each other.

(astrology) Denoting the aspect of two celestial bodies which are 120° apart.

(astrology) An aspect of two planets with regard to the Earth when they are three octants, or three eighths of a circle (135 degrees), distant from each other.

(geography) The parallel of latitude 23°30′north of the equator, marking the northern boundary of the tropics; the sun is directly overhead at the June solstice.

(astronomy) The moment when the sun appears to cross the celestial equator while tilting towards from the observer, taking place in March in the northern hemisphere and September in the southern hemisphere.

The point on the ecliptic where the sun crosses from the southern celestial hemisphere to the northern, which occurs at the (northern) vernal equinox; less commonly, either this point or the opposite point of crossing from north to south.

(astrology) The point where the prime vertical meets the ecliptic in the western hemisphere of a natal chart.

(astronomy) A great circle on the celestial sphere, perpendicular to the horizon, that passes through the zenith and nadir

(astronomy) The moment when the Earth is in that point of its orbit where the northern or southern hemisphere is most inclined away from the sun.

Alternative form of zenithal passage [The passing of the sun directly overhead such that no shadows are cast by a pole sticking straight up from the ground. These conditions only occur in locations between the Tropic of Cancer and the Tropic of Capricorn.]

The passing of the sun directly overhead such that no shadows are cast by a pole sticking straight up from the ground. These conditions only occur in locations between the Tropic of Cancer and the Tropic of Capricorn.

Archaic spelling of Equator. [(geography) Earth’s equator.]

Obsolete spelling of equinoctial [The great circle midway between the celestial poles; the celestial equator.]

Obsolete spelling of equinox [One of the two occasions in the year when the length of the day and night are equal, which occurs when the apparent path of the Sun (the ecliptic) intersects with the equatorial plane of the Earth; this happens on a day between March 19 and 21 (spring in the Northern Hemisphere, and autumn in the Southern Hemisphere), and on another day between September 21 and 24 (autumn in the Northern Hemisphere, and spring in the Southern Hemisphere); hence, the exact time when the intersection occurs.]