Topic IV: Motions of the Earth, Moon and Sun

Learning Objectives EARTH’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 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 Simulation

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. Season Date Sun Rise Sun Set Daylight hrs. Due West Fall 9/23 Due East 12hrs. Winter 12/21 South of East South of West <12hrs. Spring 3/21 12hrs. Due East Due West Summer >12hrs. 6/21 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 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 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 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: Foucault pendulum 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? 15o 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 Phases 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

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 Explanation 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 Explanation Real Life