Earth
One of the four periods of the year, beginning astronomically at an equinox or solstice, but geographically at different dates in different climates
season
The figure of the moon in its first or last quarter, resembling a segment of a ring tapering to points at the ends.
Cresent
To supply or brighten with light; light up.
Illuminate
The tide at the point of maximum ebb or the time of low water.
Low Tide
The obscuration of the light of the moon by the intervention of the earth between it and the sun or the obscuration of the light of the sun by the intervention of the moon between it and a point on the earth.
Eclipse
The line about which a rotating body, such as the earth, turns.
Axis
The instant, approximately one week after a full moon, when half of the moon's disk is illuminated by the sun.
Last/Third Quarter Moon
The motion of an object around a point, especially around another object or a center of mass.
Revolution
The tide at its highest level of elevation or the time of high water.
High Tide
The time when the sun crosses the plane of the earth's equator, making night and day of approximately equal length all over the earth.
Equinox
The great circle formed by the intersection of the plane of the earth's orbit with the celestial sphere; the apparent annual path of the sun in the heavens.
Ecliptic
The moon at any time after the new moon and before the full moon, so called because its illuminated area is increasing.
Waxing Moon
The average distance between the Sun and the Earth's orbit.
Solar Distance
A tide in which the difference between high and low tide is the least.
Neap Tide
An astronomical body that orbits a planet, dwarf planet, or small Solar System body.
Natural Satellite
The point in the orbit of a heavenly body, especially the moon, or of a man-made satellite at which it is farthest from the earth.
Apogee
The moon at any time after the full moon and before the new moon, so called because its illuminated area is decreasing.
Waning Moon
Either of the two times a year when the sun is at its greatest distance from the celestial equator.
Solstice
Difference in height between high tide and low tide.
Tidal Range
A partial shadow between regions of full shadow and full illumination during an eclipse.
Penumbra
The point in an orbit that is nearest to the body being orbited.
Perigee
Convex at both edges, as the moon when more than half full.
Gibbous
The point in the orbit of a planet or comet at which it is nearest to the sun.
Perihelion
The large rise and fall of the tide at or soon after the new or the full moon.
Spring Tide
An alignment of three celestial objects, as the sun, the earth, and either the moon or a planet.
Syzygy