1.
Accretion theory: The uniformitarian theory that all celestial objects, but especially those of the solar system, were formed by the gravitational accumulation of space dust.
2.
Annual eclipse: An eclipse of the sun in which a narrow ring (annulus) of the sun's disk shows around the moon because the moon is too far from the earth to cover the sun's disk completely.
3.
Apogee: The point in the orbit of the moon or a man made satellite where it is farthest from Earth.
4.
Baily's beads: Bright pinpoints of light that appear briefly during a total solar eclipse as sunlight shines through valleys around the moon's edge
5.
Capture theory: The naturalistic theory that the moon was once a planet in its own orbit around the sun but that the earth somehow deflected it into an orbit around the earth
6.
Cusp: A pointed end of a crescent moon.
7.
Diamond ring effect: During a total solar eclipse, the effect produced by a single Baily's bead flash occurring along the thin remaining solar crescent at the limb of the moon. It occurs immediately before or after totality in a solar eclipse
8.
Earthshine: Sunlight reflected from the dark side of the moon that was originally reflected from the earth.
9.
Escape velocity: The initial speed an object must have in order to free itself from the gravitational pull of a planet or other celestial body.
10.
First quarter: The phase of the moon when the western half of the moon is lighted and the eastern half is dark.
11.
Fission theory: A naturalistic theory of the origin of the moon suggesting that somehow the moon split away from the earth when the earth was still molten
12.
Force: A push or a pull exerted on an object. A force may may be transmitted by contact between two objects or exerted over a distance between objects.
13.
Full moon: The lunar phase in which the moon's entire near side is lighted.
14.
Harvest moon: The full moon nearest the autumnal equinox (about September 22 in the Northern Hemisphere).
15.
Hunter's moon: The next full moon after the harvest moon.
16.
Impact theory: A naturalistic theory for the origin of the moon that suggests the matter in the moon was once a part of the earth, but a collision with another celestial object ejected the matter from the earth, and some of the matter coalesced and went into orbit around the earth as the moon.
17.
Last quarter: Same as third quarter.It is that phase of the moon in which the eastern half is lighted and the western half is dark.
18.
Lunar eclipse: The darkening of the full moon when it passes into the Earth's shadow.
19.
Mare: A dark,flat lowland region on the moon's surface.
20.
Mass: A measure of the amount of matter an object contains;not dependent on the force of gravity.
21.
New moon: That phase of the moon when it is positioned in its orbit between the sun and the earth and is not visible because of the sun's glare
22.
Partial eclipse: An eclipse in which the face of the sun is never fully covered, as observed at a particular location.
23.
Perigee: The point nearest the earth in the orbit of the moon or of an earth-orbiting satellite.
24.
Ray: Any of the bright streaks on the moon's surface radiating from some of the moon's craters.Also, a high energy electromagnetic wave emitted by an atom or its nucleus.
25.
Rills: Long,narrow,snaking valleys especially evident on the moon's surface.
26.
Solar eclipse: An eclipse that occurs when the moon passes between the earth and the sun,blocking some or all of the sun's light to the earth at a given location.
27.
Terminator: The line dividing the lighted portion of a non luminous celestial body from the dark portion.
28.
Third quarter: Same as last quarter. It is that phase of the moon in which the eastern half is lighted and the western half is dark.
29.
Total eclipse: An event where the direct (solar) or reflected (lunar) light from the sun as viewed by an observer at a given location is completely cut off by another astronomical body.
30.
Waning crescent: The decreasing phase of the moon,following a full moon,when the illuminated disk gradually diminishes to the third quarter.
31.
Waning gibbous: The decreasing phase of the moon,following a full moon,when the illuminated disk gradually diminishes to the third quarter.
32.
Waxing crescent: The increasing phase of the moon,during the week following a new moon,when its illuminated portion appears as a thin, gradually thickening crescent.
33.
Waxing gibbous: The increasing phase of the moon,during the second week following the first quarter, when the illuminated portion is gradually enlarging toward a full moon.
