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25 Cards in this Set

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apogee
point in which the orbit of a planet at which the planet is farthest from the sun
calendar
system used to measure the passage of time.
crater
bowl-shaped depression on the surface of a planetary body.
day
time required for the earth to make one rotation on it's axis, about 24 hours.
earthshine
sunlight reflected off the surface of the earth.
eclipse
passing of one planetary body through the shadow of another.
full moon
phase of the moon in which the entire half of the moon facing the earth is visible.
Galilean moon
any one of the four largest satellites of Jupiter, which were first seen by Galileo.
Gregorian calendar
revision of the Julian calendar by Pop Gregory XIII; currently used in most of the world.
leap year
year with an extra day in it, occuring every four years.
lunar eclipse
passing of the earth between the moon and the sun during which the earth's shadow crosses the lighted half of the moon.
maria
dark areas of smooth, dry,solidified lava on the moon that reflect little light.
month
time required for the moon to go through one set of phases as it orbits the earth, about 29.5 days.
new moon
phase of the moon during which the side of the moon facing the earth is unlighted.
penumbra
outer part of the shadow cast by the earth or the moon in which sunlight is only partially blocked.
Julian calendar
calendar designed by Julius Caesar's astronomers consisting of 12 months; 11 with 30 or 31 days, one with 28 days, and an extra day added every four years.
perigee
point in the orbit of a satellite at which it is closest to the earth.
phase
varying shape of the visible portion of the moon.
ray
streak of displaced rock material radiating from a crater.
rille
long, deep channel that runs through the maria on the moon.
solar eclipse
passing of the moon between the earth and the sun during which the shadow of the moon falls on the earth.
solar year
time required for the earth to mkae one orbit around the sun, about 365.24 days.
umbra
inner, cone-shaped part of the shadow cast by the earth or the moon in which sunlight is completely blocked.
waning
describing the phase of the moon during which the size of its visible portion is decreasing.
waxing
describing the phase of the moon during which the size of its visible portion is increasing.