The Earth-Moon-Sun System Unit 3: Astronomy Chapter 7: The Earth-Moon-Sun System

Chapter 7: The Earth-Moon-Sun System UNIT 3: Chapter 7: The Earth-Moon-Sun System I. Earth in Space A. Earth’s Size and Shape   1. Early astronomers like Aristotle said Earth was spherical in shape a. Evidenced by shadow of Earth on Moon during eclipse b. People in different parts of world see different stars above their horizons

2. Curvature of Earth is evident when looking at objects far away  

3. Modern images of the Earth from space  

4. Gravity was force that caused it to form spherical shape as Earth formed.  

5. Earth’s Physical Properties  

B. Earth’s Magnetic Field 1. Earth has magnetic field similar to a bar magnet a. Protects us from harmful radiation from Sun b. Magnetic field concentrated at the poles

2. Location of poles changes slowly over time 3. Aurora borealis (northern lights) caused by reaction of charged particles from sun and Earth’s magnetic field  

C. Earth Orbits the Sun 1. Earth orbits the Sun in an elliptical orbit (“squashed circle”)

a. Distance of Earth to sun varies during year b. Closest to the Earth in January and furthest away in July  

2. Earth is considered a planet like Venus, Mars, and Jupiter.   a. Conditions on different planets depend on how far from the Sun they are and their size b. Mars is most like the Earth

II. Time and Seasons A. Measuring Time on Earth 1. People have used the position and movements of Sun and Moon to measure time for thousands of years

2. Earth’s movements measure time a. Earth spins and makes one complete rotation every 24 hours.

b. Earth spins 360° in 24 hours- equals 15° every hour.

c. This led to time zones every 15°

d. International Date Line- falls down through the Pacific Ocean.

3. The spinning (rotation) motion of Earth enables you to measure the passing hours of the day. 4. The motion (revolution) of Earth around the Sun enables you to measure passing of years  

B. Why do Seasons change? 1. The distance between the Earth and the Sun varies throughout the year.

2. Seasons caused by Earth’s rotation, its revolution, and the tilt of its axis (23.5°)

3. Angle at which sunlight hits the Earth determines warming effect a. Higher angles produce more warming b. Lower angles produce less warming

4. More hours of sunlight in summer than winter 5. Equinox- when number of daylight hours equals number of nighttime hours a. Spring equinox- March 21st b. Fall equinox- September 22

6. Solstice- sun reaches greatest distance north or south of equator a. Summer solstice- June 21st b. Winter solstice- December 21st

 III. Earth’s Moon A. Movement of the Moon 1. The Moon revolves around the Earth every 27.3 days (a sidereal month) 2. The same side of the moon faces Earth because it also rotates one complete revolution in 27.3 days

B. How does the Moon affect the Earth? 1. Tides- caused by gravitational pull of the Sun and Moon a. Moon’s gravity has more effect than Sun because it is much closer to Earth b. As Earth rotates, different locations pass through high and low tides

C. Moonlight 1. Moon phases- are changing appearances of the Moon as seen from Earth a. New Moon- occurs when Moon is between Earth and Sun. Moon is in sky,but cannot be seen

b. Waxing phases- occurs after new moon b. Waxing phases- occurs after new moon. Lighted portion becomes larger each night

c. Waning phases- Lighted portion begins to get smaller

d. Full Moon- occurs when we see all of Moon’s lighted side

2. The word month comes from the same root word as Moon

D. Eclipses   1. Solar eclipses- occurs when Moon moves directly between Sun and Earth and casts shadow on part of Earth

2. Lunar eclipse- occurs when Earth’s shadow falls on the Moon

E. The Moon’s Surface 1. Moon’s surface includes many different surface features 2. Craters- depressions on the Moon formed by impact of meteorites, asteroids, and comets  

3. Maria- dark-colored, relatively flat regions formed by igneous rocks 93 to 4 billion years old)

4. Regolith- few centimeters thick to over 40 m thick 4. Regolith- few centimeters thick to over 40 m thick. Various from coarse to dust-like

F. Moon’s Interior- Model shows crust 60 km - 150 km thick with solid mantle 1000 km deep with partially molten core

G. Exploring the Moon- has included both manned and non-manned spacecraft

H. Origin of the Moon 1. Prior to Apollo mission there were 3 different theories 2. After Apollo mission all three theories found incorrect

3. Led to new theory- Giant Impact Theory a. Moon formed 4.6 billion years ago b. Mars sized object collided with Earth c. Debris thrown into orbit and condensed into large mass, forming the moon d. Moon’s composition likes Earth’s mantle