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Topic IV: Motions of the Earth,
Moon and Sun
Learning Objectives
 Explain and demonstrate the difference between rotation
and revolution.
 Be able to calculate the rate of rotation and the
movement of celestial objects through the sky.
 Be able to explain the motion of Polaris in the sky as well
as the motion of constellations.
 Provide evidence for the Earth’s rotation---Focault
Pendulum and Coriolis Effect specifically.
 Provide evidence for Earth’s revolution---different
constellations through the year, specifically
Learning Objectives
 Draw the eight phases of the moon.
 Explain that the phases of the moon are caused by the
moon’s revolution around the Earth.
 Explain that the tides are caused the by the gravitational
attraction of the moon and the sun.
 Explain the difference between neap and spring tides
and during which phases of the moon each occurs.
 Explain the difference between lunar and solar eclipses
and during which phases of the moon each can occur.
 Explain why the moon rises 50 minutes later each day.
Apparent Motions of Celestial Objects
Apparent motions: Motions that an object appears to make
Apparent motion of the sun: Rises in the east and sets in
the west
Apparent Motions of The Stars
Looking East: Stars rise out of the east
Looking West: Stars set in the west
Looking North: Circle the north star
Looking South: Rise in the SE and set in the SW
Star Trails
Apparent Motion of the Planets
Retrograde Motion: Apparent backward motion of planets
Why does it happen: Earth passes outer planets in orbit
Apparent Motion of Earth’s Moon
Rises: In the east Sets:In the west Daily difference: 50min
Apparent Motions of the Sun
Rises: In the east
Sets: In the west
What are some changes that occur throughout the year?
Apparent Motions of the Sun Contd.
Sun Rise
Sun Set
Daylight hrs.
Due East
Due West
South of East
South of West
Due East
Due West
North of East
North of West
Solstice: (Sun stop) sun stops increasing or decreasing in
altitude. 12/21 and 6/21
Equinox: (Equal night) 12hrs. Of light and dark all over earth.
3/21 and 9/23
What causes the seasons
Changes in the Altitude of the Sun at Noon
Solar noon: Time of day when sun is highest
Where is the sun directly overhead on
the following dates?
Sept. 23: Equator
Dec. 21: Tropic of Capricorn
Mar. 21: Equator
Jun. 21: Tropic of Cancer
Models That Help to Explain Celestial
Geocentric Models: Earth centered, planets revolve around a
stationary earth.
What is good about the geocentric?
1) Explains motions of the sun and
other stars
2) The church endorsed it
What was bad?
1) Didn’t explain retrograde motion
2) Didn’t explain Coriolis or Foucault
3) Models should be simple (epicycles)
Heliocentric Models
Heliocentric Models: Sun centered, planets rotate and revolve
around a stationary sun
What is good about the
1) Explained retrograde motion
2) Explained Coriolis and
What was bad?
1) Said orbits were perfect circles
2) Church was against it
Actual Earth Movements
Rotation: Spin of earth on its axis
Axis: Imaginary line that goes through the poles
Does our axis tilt? Yes at a 23.5o angle
What is the rate of rotation?
15 degrees per hour
What direction does earth
rotate? From west to east or
counterclockwise from
N. pole
Actual Earth Movements
Evidence of rotation: 1) Foucault pendulum
2) Coriolis effect
Actual Earth Movements
Revolution: Going around the sun in an orbit
What is the true shape of planet orbits? Ellipse
Formula: Distance Between Foci
Length of Major Axis
Evidence of Revolution
1) Constellations changes
2) Diameter of the sun changes
When are we farthest from the sun? Summer
Earth and Moon Motions and Time
Local time: Time based on earth’s rotation
What can be said about local time of places on the same
meridian? They have the same local time
Local solar time: Time based on the position of the sun
What instrument is used to measure solar time? Sundial
Time Zone or Standard Time
How far apart are time zones?
As you move east what happens to local time? Gets later
Where is standard time based from? Greenwich England
Time Zones
Actual Motions of Earth’s Moon
Revolution: Period of revolution is 27 1/3 days
Moon’s orbit: Tilted at a 5o angle
Moon Phases
How much of the moon is lit
everyday? 1/2
What is the relationship between phases and time? Cyclic
Waxing: Bright on right and getting bigger
Waning: Bright on left and getting smaller
Period of Revolution: 27 1/3 days
From full to full: 29 1/2
Why is the cycle time different from the period of
revolution? Moon has to catch up to earth
Cool Trick
What causes tides? The gravitational pull of the moon
High tide: Higher than normal shoreline
Low tide: Lower than normal shoreline
Role of the sun: Strengthens or
weakens the tides
Spring tides: Higher tide range
Neap tides: Lower tide range
Lunar Eclipse: Earth casts a shadow on the moon
How many a year? 2-4 times per year
Why aren’t all full moons eclipses? Tilt of moon orbit
Solar Eclipse
Solar Eclipse: The moon blocks the light from the sun
How often: Once every 200 years or so
Real Life