Rotation vs. Revolution
Rotation The amount of time it takes for Earth to
spin around once. ONE DAY
Revolution The amount of time it takes for Earth to
go around the Sun once. ONE YEAR
Movements in Orbit
Perigee At its closest point in orbit▪ Object appears large
Apogee At its farthest point in orbit▪ Object appears small
What do they all do?
Sun Provides light,
warmth Source of most of
energy that fuels our society
Moon Raises tides in
ocean Illuminates sky with
monthly cycle of phases
Rotation & Length of Day
Length of day is a little longer than the time it takes Earth to rotate once on its axis. As Earth rotates, it also moves in its
orbit▪ It has to turn a little farther
Solar Day The time period from one sunrise or
sunset to the next▪ Our timekeeping system is based on the solar
day
Annual Motions
Length of day and temps may range depending on latitude What is latitude?
Annual changes are due to Earth’s orbital motion around the Sun Earth’s orbit is in an ecliptic plane▪ Oval-shaped
The Moon
Does not emit visible light Reflection of the Sun’s light
Phases of the Moon The changes of position in the sky is a result of
the movement of the moon around the Earth Lunar Phases▪ The sequential changes in appearance of the moon
Waxing Increase in portion of sunlight side of the moon
Waning Decrease in amount of sunlit side of the Moon
Phases of the Moon
New Moon Moon is between Earth and Sun Dark side of the moon faces Earth
Waxing Crescent Less than half the lit portion during
increaseFirst Quarter
Half the sunlit side during increase
Phases of the Moon (cont’d)
Waxing Gibbous More than half of the lit portion during
increaseFull Moon
Earth is between Moon and Sun Can see entire sunlit side of moon
Waning Gibbous More than half the lit portion during
decrease
Phases of the Moon (cont’d)
Third Quarter Half the sunlit side during decrease
Waning Crescent Less than half the lit portion during
decreaseNew Moon
Beginning of cycle again
Moon Rotation
As the moon orbits, the same side always faces Earth at all times It spins exactly once each time it orbits
EarthLunar Month
The length of time it takes for 1 complete cycle of phases▪ About 29.5 days
Tides
The moon’s gravity pulls on Earth Creates bulges of ocean water on near
and far sides of Earth
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