Bellringer
How many forces are acting on a baseball that is
thrown by a pitcher?
Phases, Eclipses,
and Tides
Notes
Lunar
Motions
• Our moon’s name = Luna
• The changing relative positions of the
moon, Earth, and sun cause the phases
of the moon, eclipses, and tides.
• Luna revolves around the Earth. It takes
the moon about 27.3 days to revolve
around Earth once.
• As Luna and Earth move, their positions
change in relation to each other. Their
positions also change in relation to the
sun.
Lunar Motion
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Our moon it tidally locked with Earth.
This means that the moon’s day is the
same as its year. It takes one month to
rotate on its axis and one month to
complete one revolution around Earth.
Because of this, only one side of Luna
faces Earth. The other side is ALWAYS
facing away from Earth.
There is no such thing as the “dark side” of
the moon, but there is a “far side.”
Lunar Phases
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The phase of the moon you see depends on
how much of the sunlit side of the moon
faces Earth.
The moon does not give off its own light. The
moon reflects light from the sun.
Question: How much of the moon is
ALWAYS lit up by the light from the sun?
Question 2: How much of every object in this
solar system is ALWAYS lit up by the sun?
Phases of the Moon
• The moon appears to have different
shapes at different times. These
different shapes of the moon that you
see are called phases.
Lunar Phases
•As the moon revolves around Earth, you
see the moon from different angles. You
cannot see all of the half of the moon that
is lit by the sun.
•http://upload.wikimedia.org/wikipedia/co
mmons/c/c0/Lunar_libration_with_phase
2.gif
Lunar Phases
1.New Moon
•Waxing - Getting Bigger
(wax on)
2.Waxing Crescent
3.First Quarter
4.Waxing Gibbous
•Waning - Getting Smaller
(wane off)
•Crescent - less than 1/4
visible
5.Full Moon
6.Waning Gibbous
7.Third Quarter
•Gibbous - more than 1/4
visible
•All 8 phases occur within
about one month’s time.
8.Waning Crescent
Eclipses
• Eclipse - to cover up
• When Luna’s shadow hits Earth or
Earth’s shadow hits Luna, an eclipse
occurs. A solar eclipse occurs when the
moon passes directly between Earth
and Sol, blocking sunlight from Earth.
• An eclipse is when an object in space
comes between the sun and another
object.
Eclipses
• Sometimes the moon moves between
Earth and Sol. The moon blocks
sunlight from reaching Earth (this
means the moon is casting its shadow
onto the surface of Earth). A solar
eclipse occurs when an NEW MOON
blocks your view of the sun.
Eclipses
• A lunar eclipse occurs when Earth is
between Luna and Sol.
• In a lunar eclipse, Earth’s shadow hits
the moon.
• A lunar eclipse occurs when there is a
FULL MOON.
Eclipses
•So why is there not a solar and lunar
eclipse each time we have a NEW
MOON and FULL MOON?
•The moon does not lie in a straight line
between Earth and Sol. It is tilted about
5° from the ecliptic. Because of this tilt,
eclipses are much rarer than expected.
•http://eclipse.gsfc.nasa.gov/eclipse.html
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Tides
Tides are caused mainly by differences in how
much Luna’s gravity pulls on different parts of
Earth.
Tides are the regular rise and fall of ocean water.
The ocean waters rise for about 6 hours a day,
and fall for about 6 hours a day. Therefore there
are two high tides and two low tides every 24
hours.
Luna’s gravity causes tides. The force of the
moon’s gravity causes ocean water on Earth to
move higher in some places and lower in other
places.
Sol’s gravity also pulls on Earth’s ocean waters.
Tides
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During a NEW MOON, Sol, Earth, and Luna
are lined up in a straight line. The combined
forces of the sun and the moon cause
spring tides. A spring tide is the highest
possible high tide.
Sometimes the sun, moon, and Earth form a
right angle (90°). This arrangement occur at
the FIRST and THIRD QUARTER moons,
and produces a neap tide. A neap tide is
the lowest possible high tide.