Astronomy Ch.1

Front 1

accelerate

Back 1

To change velocity; to speed up, slow down, or change direction

Front 2

asterism

Back 2

An especially noticeable star pattern in the sky, such as the Big Dipper.

Front 3

astrology

Back 3

The pseudoscience that deals with the supposed influences on human destiny of the configurations and locations in the sky of the Sun, Moon, and planets; a primitive belief system that had its origin in ancient Babylonia.

Front 4

axis

Back 4

An imaginary line about which a body rotates.

Front 5

azimuth

Back 5

The angle along the celestial horizon, measured eastward from the north point to the intersection of the horizon with the vertical circle passing through an object.

Front 6

celestial equator

Back 6

A great circle on the celestial sphere 90° from the celestial poles; where the celestial sphere intersects the plane of the Earth's equator.

Front 7

celestial meridian

Back 7

An imaginary line on the celestial sphere passing through the north and south points on the horizon and through the zenith.

Front 8

celestial poles

Back 8

Points about which the celestial sphere appears to rotate; intersections of the celestial sphere with the Earth's polar axis.

Front 9

celestial sphere

Back 9

Apparent sphere of the sky; a sphere of large radius centered on the observer. Directions of objects in the sky can be denoted by their position on the celestial sphere.

Front 10

circumpolar zone

Back 10

Those portions of the celestial sphere near the celestial poles that are either always above or always below the horizon.

Front 11

compound

Back 11

A substance composed of two or more chemical elements.

Front 12

ecliptic

Back 12

The apparent annual path of the Sun on the celestial sphere.

Front 13

element

Back 13

A substance that cannot be decomposed by chemical means into simpler substances.

Front 14

epicycle

Back 14

A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle (the deferent).

Front 15

equator

Back 15

A great circle on the Earth, 90° from (or equidistant from) each pole.

Front 16

geocentric

Back 16

Centered on the Earth.

Front 17

heliocentric

Back 17

Centered on the Sun.

Front 18

horizon (astronomical)

Back 18

A great circle on the celestial sphere 90° from the zenith; more popularly, the circle around us where the dome of the sky meets the Earth.

Front 19

horoscope

Back 19

A chart used by astrologers, showing the positions along the zodiac and in the sky of the Sun, Moon, and planets at some given instant and as seen from a particular place on Earth - usually corresponding to the time and place of a person's birth.

Front 20

magnitude

Back 20

A system of measuring the amount of light flux received from a star or other luminous object. The higher the magnitude, the less radiation we receive from the object.

Front 21

planet

Back 21

Any of the nine largest objects revolving about the Sun, or any similar objects that orbit other stars. Unlike stars, planets do not (for the most part) give off their own light but only reflect the light of their parent star.

Front 22

planetarium

Back 22

An optical device for projecting on a screen or domed ceiling the stars and planets and their apparent motions in the sky.

Front 23

precession (of Earth)

Back 23

A slow, conical motion of the Earth's axis of rotation caused principally by the gravitational pull of the Moon and Sun on the Earth's equatorial bulge.

Front 24

precession of the equinoxes

Back 24

Slow westward motion of the equinoxes along the ecliptic that results from precession.

Front 25

retrograde (rotation or revolution)

Back 25

Backward with respect to the common direction of motion in the solar system; clockwise as viewed from the north, and going from east to west rather than from west to east.

Front 26

retrograde motion

Back 26

An apparent westward motion of a planet on the celestial sphere or with respect to the stars.

Front 27

sign (of zodiac)

Back 27

Astrological term for any of 12 equal sections along the ecliptic, each of length 30°. Because of precession, these signs today are no longer lined up with the constellations from which they received their names.

Front 28

year

Back 28

The period of revolution of the Earth around the Sun.

Front 29

zenith

Back 29

The point on the celestial sphere opposite to the direction of gravity; the point directly above the observer.

Front 30

zodiac

Back 30

A belt around the sky about 18° wide centered on the ecliptic.