phase - (astronomy) the particular appearance of a body's state of illumination (especially one of the recurring shapes of the part of Earth's moon that is illuminated by the sun); "the full phase of the moon"

absolute magnitude - (astronomy) the magnitude that a star would have if it were viewed from a distance of 10 parsecs (32.62 light years) from the earth

Hubble law, Hubble's law - (astronomy) the generalization that the speed of recession of distant galaxies (the red shift) is proportional to their distance from the observer

Kepler's law, Kepler's law of planetary motion - (astronomy) one of three empirical laws of planetary motion stated by Johannes Kepler

natural philosophy, physical science, physics - the science of matter and energy and their interactions

astrodynamics - the branch of astronomy that studies the motion of natural and artificial bodies in space

astrometry - the branch of astronomy that deals with the measurement of the position and motion of celestial bodies

radio astronomy - the branch of astronomy that detects and studies the radio waves emitted by celestial bodies

celestial mechanics - the branch of astronomy concerned with the application of Newton's laws of motion to the motions of heavenly bodies

astrophysics - the branch of astronomy concerned with the physical and chemical properties of celestial bodies

solar physics - the branch of astronomy that deals with the sun

ascension - (astronomy) the rising of a star above the horizon

egress, emersion - (astronomy) the reappearance of a celestial body after an eclipse

ingress, immersion - (astronomy) the disappearance of a celestial body prior to an eclipse

alignment, conjunction - (astronomy) apparent meeting or passing of two or more celestial bodies in the same degree of the zodiac

inferior conjunction - (astronomy) the alignment of the Earth and a planet on the same side of the sun

superior conjunction - (astronomy) the alignment of the Earth and a planet on the opposite side of the sun

Oort cloud - (astronomy) a hypothetical huge collection of comets orbiting the sun far beyond the orbit of Pluto; perturbations (as by other stars) can upset a comet's orbit and may send it tumbling toward the sun

extragalactic nebula, galaxy - (astronomy) a collection of star systems; any of the billions of systems each having many stars and nebulae and dust; "`extragalactic nebula' is a former name for `galaxy'"

apoapsis, point of apoapsis - (astronomy) the point in an orbit farthest from the body being orbited

node - (astronomy) a point where an orbit crosses a plane

equinoctial point, equinox - (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic

vernal equinox - (astronomy) the equinoctial point that lies in the constellation of Pisces

autumnal equinox - (astronomy) the equinoctial point that lies in the constellation of Virgo

barycenter - (astronomy) the common center of mass around which two or more bodies revolve

culmination - (astronomy) a heavenly body's highest celestial point above an observer's horizon

limb - (astronomy) the circumferential edge of the apparent disc of the sun or the moon or a planet

periapsis, point of periapsis - (astronomy) the point in as orbit closest to the body being orbited

anomaly - (astronomy) position of a planet as defined by its angular distance from its perihelion (as observed from the sun)

asterism - (astronomy) a cluster of stars (or a small constellation)

canal - (astronomy) an indistinct surface feature of Mars once thought to be a system of channels; they are now believed to be an optical illusion

coma - (astronomy) the luminous cloud of particles surrounding the frozen nucleus of a comet; forms as the comet approaches the sun and is warmed

comet - (astronomy) a relatively small extraterrestrial body consisting of a frozen mass that travels around the sun in a highly elliptical orbit

meteoroid, meteor - (astronomy) any of the small solid extraterrestrial bodies that hits the earth's atmosphere

nucleus - (astronomy) the center of the head of a comet; consists of small solid particles of ice and frozen gas that vaporizes on approaching the sun to form the coma and tail

star - (astronomy) a celestial body of hot gases that radiates energy derived from thermonuclear reactions in the interior