Astronomy: The study of outer space. [The branch of science which deals with the part of the Universe that lies beyond the Earth's atmosphere.]
Axis: A straight line, real or imaginary, passing through a body, around which it spins (rotates). The Earth's axis is tilted 23.5 degrees.
Rotation: Turning of a body about an imaginary axis running through it. The Earth rotates counterclockwise once every 24 hours (one day), causing day and night.
Revolution: The motion of one body around another. The Earth revolves counterclockwise around the Sun once every 365 days (one year). Orbit is a synonym for revolution. (Remember that synonyms are two words which have the same meaning.)
Star: A self-luminous sphere of gas (mostly hydrogen and helium).
Sun: The star around which the Earth and the other planets in our Solar System revolve. The Sun is a medium-sized star; it appears larger than other stars because it is the star nearest to Earth. The diameter of the Sun is more than 100 times larger than the Earth's diameter; more than a million Earths would fit inside the Sun's volume!
Planet(s): Any of the nine solid bodies revolving about the Sun.
Earth: The third planet from the Sun in the Solar System. Our home planet.
Moon: A natural satellite that revolves around a planet. For example, "the Moon" revolves around the Earth approximately once every 30 days (one month). The diameter of the Moon is about 1/4 the Earth's diameter.
Terminator: The line of sunrise or sunset on a moon or a planet.
Phases of the Moon: The progression of changes in the Moon's appearance during the month that results from the Moon's turning different portions of its illuminated hemisphere to our view.
New Moon: Phase of the Moon when it's longitude is the same as that of the Sun.
Waxing Crescent: One of the phases of the Moon when its elongation is less than 90 degrees from the Sun and it appears to be less than half full (the right side is illuminated).
First Quarter: One of the two phases of the Moon when its longitude differs by 90 degrees from that of the Sun; the Moon appears half full at these phases (the right half is illuminated).
Waxing Gibbous: One of the phases of the Moon in which more than half, but not all, of the Moon's daylight hemisphere is visible from the Earth (the right side is illuminated).
Full Moon: The phase of the Moon when it is at opposition (180 degrees from the Sun) and its full daylight hemisphere is visible from the Earth.
Waning Gibbous: One of the phases of the Moon in which more than half, but not all, of the Moon's daylight hemisphere is visible from the Earth (the left side is illuminated).
Last Quarter: One of the two phases of the Moon when its longitude differs by 90 degrees from that of the Sun; the Moon appears half full at these phases (the left half is illuminated).
Waning Crescent: One of the phases of the Moon when its elongation is less than 90 degrees from the Sun and it appears to be less than half full (the left side is illuminated).
Waxing: To grow.
Waning: To shrink.
Month: Calendar time unit derived from the approximate time for the Moon to go through one cycle of phases.
Solar Eclipse: The cutting off of all or part of the light from the Sun by the Moon passing in front of it.
Lunar Eclipse: The cutting off of all or part of the sunlight reflected from the Moon by the Earth passing between the Sun and the Moon.
Total Eclipse: An eclipse of the Sun in which the Sun's photosphere is entirely hidden by the Moon, or an eclipse of the Moon in which it passes completely into the umbra of the Earth's shadow.
Partial Eclipse: An eclipse of the Sun or Moon in which the eclipsed body does not appear completely obscured.
Umbra: The central, completely dark part of a shadow.
Penumbra: The portion of a shadow from which only part of the light source is occulted by an opaque body.
Ocean Tides: The deformation of the ocean surface by the differential gravitational forces exerted by the Moon and the Sun.
Barycenter: The center of mass of two mutually revolving bodies.
High Water (High Tide): The maximum height reached by a rising tide. The high water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions.
Low Water (Low Tide): The minimum height reached by a falling tide. The low water is due to the periodic tidal forces and the effects of meteorological, hydrologic, and/or oceanographic conditions.
Tidal Range: The difference in height between consecutive high and low waters. The mean range is the difference in height between mean high water and mean low water. The great diurnal range or diurnal range is the difference in height between mean higher high water and mean lower low water.
Spring Tide: The highest ocean tidal range of the month, produced when the Moon is near either the Full or New phase.
Neap Tide: The lowest-ranging ocean tide during the month, which occurs when the Moon is near First or Last Quarter.
Seasons: Winter, Spring, Summer, or Fall (all you gotta do is call)
Equinox: One of the intersections of the ecliptic and the celestial equator. [One of two dates when the noon Sun would be at the zenith along the Equator of the Earth. Literally means, "equal nights," as in the number of hours of daylight and darkness are approximately equal.]
Solstice: Either of two points on the celestial sphere where the Sun reaches its maximum distances north and south of the celestial equator. [Literally means, "Sun stop," as in the line of latitude on the Earth's surface along which the noon Sun would be at the zenith stops moving northward or southward.]
Perihelion: The point in the path of a celestial body (as a planet) that is nearest to the Sun.
Aphelion: The point in the path of a celestial body (as a planet) that is farthest from the Sun.