Astronomical Terms

ABERRATION OF STARLIGHT

Apparent change in the position of a star

APHELION

Point at which an object in solar orbit is farthest from the Sun

APOGEE

Point at which an orbiting object is farthest from the Earth

ARMILLARY SPHERE

Model with rings, used to show relationships among the circles on the celestial sphere

ASTROLABE

Medieval instrument consisting of a graduated vertical circle with a moveable arm, used to determine the altitude of celestial bodies

AZIMUTH

Horizontal bearing of a celestial object measured clockwise from a given direction

CELESTIAL SPHERE

Imaginary sphere around the Earth on which celestial bodies are assumed to lie, for the purpose of finding or identifying their position

CONJUNCTION

Occasion when two celestial bodies line up on the celestial sphere

DECLINATION

Angular measure of a star's position, measured in degrees north and south of the celestial equator

ECLIPTIC

Great circle on the celestial sphere representing the apparent annual path of the Sun relative to the stars

EQUINOX

Instant when the Sun lies directly overhead at the Equator

NADIR

Point in the heavens diametrically opposite the zenith, or directly under an observer

ORRERY

Mechanical model of the solar system

PERIGEE

Point at which an orbiting object is closest to the Earth

PERIHELION

Point at which an object in solar orbit is closest to the Sun

RED SHIFT

Lengthening of the wavelength of light from a receding celestial body

SOLSTICE

Farthest point north or south of the Equator that the Sun reaches each year

SYZYGY

Point in a celestial body's orbit at which it is either in opposition to or in conjunction with the Sun

ZENITH

Point in the heavens directly above an observer

http://en.wikipedia.org/wiki/Glossary_of_astronomy