SNC 1D1 – Motion of the Earth, Moon and Planets Earth’s Rotation

1. SNC 1D1 – Motion of the Earth, Moon and Planets • Earth’s Rotation • The apparent motion of the sun is caused by the rotation of the Earth on its axis. • In one day the earth makes one complete rotation in a west- to-east direction • When the earth faces the sun we have day, when the earth faces away from the sun we have night.

2. Earth’s Rotation About its Axis

3. Earth’s Revolution and Planetary Orbits • The earth revolves around the sun in an elliptical orbit. • Because its orbit is elliptical the distance from each planet to the sun changes as it revolves around the sun. • Astronomers calculate the average distance from the sun for each planet and call it the orbital radius. • The farther a planet is from the sun the slower a planet moves along its orbit and the longer it takes to orbit the Sun. • Mars – 687 days to orbit. • Earth - 365.25 days to orbit. • Mercury - 88 days to orbit. • Planets revolve in a counter-clockwise direction.

4. Planetary Orbits in our Solar System

5. The planets are kept in orbit around the Sun by the mass of the sun acting through gravity. • The greater the mass of an object the stronger its gravitational force. • The stronger pull of the earth on the moon keeps the moon in orbit about the earth. • The earth stays in orbit because of a balance between gravitation force and orbital velocity.

6. Demonstration of Maintaining an Orbit

7. Earth’s Tilt and the Seasons • The earth has a tilt of 23.5⁰ from the vertical. • When the earth is farthest from the Sun the northern hemisphere tilts toward the sun and the sun is concentrated on the northern hemisphere. • At this time the northern hemisphere receives the most hours of sunlight. • When the earth is closest to the sun the northern hemisphere is tilted away from the sun and the sun is concentrated on the southern hemisphere. • At this time the northern hemisphere receives the least amount of sunlight.

8. The Earth’s Seasons

9. When the earth’s axis is most inclined toward or away from the Sun, we call it a solstice. • Solstices occur twice each year on June 21 and December 21. • Between the two solstices when the hours of daylight and night are equal we have equinoxes. • Equinoxes occur on March 21 and September 21. Eclipses • Solar eclipses occur when the moon comes between the sun and the earth. The sun is blocked from being observed from the earth. • Partial solar eclipses occur when the moon does not cover the entire Sun.

10. Lunar eclipses occur when the earth is positioned between the sun and the moon casting a shadow on the moon. • If only part of the moon passes through the earth’s shadow a partial lunar eclipse occurs. Solar Eclipse Solar eclipse

11. Lunar Eclipse

12. Effect of Moon on Tides Homework: Page 328 # 1 - 14