Topic IV: Motions of the Earth, Moon and Sun

Learning ObjectivesEARTH’S MOTIONS: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 StarsLooking 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

Simulation

Apparent Motion of Earth’s Moon

Rises: In the east Sets:In the west Daily difference: 50min

Apparent Motions of the SunRises: In the east Sets: In the west

What are some changes that occur throughout the year?

Apparent Motions of the Sun Contd.

Season Date Sun Rise Sun Set Daylight hrs.

Fall

Spring

Summer

Winter

9/23

3/21

6/21

12/21

Due East

Due East

North of East

South of East South of West

North of West

Due West

Due West 12hrs.

12hrs.

<12hrs.

>12hrs.

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 Movement

Geocentric Models: Earth centered, planets revolve around a stationary earth.

What is good about the geocentric?

1) Explains motions of the sun and other stars2) 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 heliocentric?

1) Explained retrograde motion

2) Explained Coriolis and Foucault

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 changes2) 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:

What instrument is used to measure solar time?

Time based on the position of the sun

Sundial

Time Zone or Standard Time

How far apart are time zones? 15o

As you move east what happens to local time? Gets later

Where is standard time based from? Greenwich EnglandTime 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 PhasesHow 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

Phases

Cool Trick

Tides

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

Eclipses

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

Explanation

Solar Eclipse

Solar Eclipse: The moon blocks the light from the sun

How often: Once every 200 years or so

Explanation Real Life