Sphere
A round, three-dimensional object whose surface is the same distance from its center at all points;Earth is a sphere that bulges somewhat at the equator and is slightly flattened at the poles.
Axis
Imaginary vertical line that cuts through the center of Earth and around which Earth spins.
Rotation
Spinning of Earth on its imaginary axis, which takes about 24 hours to complete and causes day and night to occur.
Revolution
Earth's yearlong elliptical orbit around the Sun.
Ellipse
Elongated, closed curve that describes Earth's yearlong orbit around the Sun.
Solstice
Twice-yearly point at which the Sun reaches its greatest distance north or south of the equator.
Equinox
Twice-yearly time-each spring and fall-when the Sun is directly over the equator and the number of daylight and nighttime hours are equal worldwide.
Moon Phase
Change in appearance of the Moon as viewed from the Earth, due to the relative positions of the Moon, Earth, and Sun.
New Moon
Moon phase that occurs when the Moon is between Earth and the Sun, at which point the Moon cannot be seen because its lighted half is facing the Sun and its dark side faces Earth.
Waxing
Describes phases following a new moon, as more of the Moon's lighted side becomes visible.
Full Moon
Phase that occurs when all of the Moon's surface facing Earth reflects light.
Waning
Describes phases that occur after a full moon, as the visible lighted side of the Moon grows smaller.
Solar Eclipse
Occurs when the Moon passes directly between the Sun and Earth and casts a shadow over part of Earth.
Lunar Eclipse
Occurs when Earth's shadow falls on the Moon.
Maria
Dark-colored, relatively flat regions of the Moon formed when ancient lava reached the surface and filled craters on the Moon's surface.
Impact Basin
A hollow left on the surface of the Moon caused by an object striking its surface.