Sun, Earth, Moon Relationships

1. As long ago as 350B.C. Aristotle knew that the world was round. Earth always cast a round shadow during an eclipse

2. An axis is an imaginary line around which an object spins.

3. Rotation is the spinning of an object on its axis.

5. Earth completes 365 ¼ rotations in 1 year. 4. Earth completes 1 period of rotation in about 24 hours. 5. Earth completes 365 ¼ rotations in 1 year.

6. A revolution is the orbiting of an object around another 6. A revolution is the orbiting of an object around another. Earth completes 1 revolution in 365 days or 1 year.

7. The shape of Earth’s orbit is an ellipse.

8. Earth is closest to the sun on January 3rd at 147million km. 9. Earth is farthest from the sun on July 4th at 153 million km.

10. Earth’s axis is tilted 23½° from a line perpendicular to its orbit.

11.1 The hemisphere tilted toward the sun receives more radiation per unit area.

11.2 The hemisphere tilted toward the sun receives more hours of daylight.

12. During the fall and spring equinox the sun is directly over the equator. Spring equinox = March 21, 22 Fall equinox = September 22, 23

13. At the summer solstice the sun is over the Tropic of Cancer 13. At the summer solstice the sun is over the Tropic of Cancer. At the winter solstice the sun is over the Tropic of Capricorn. Summer solstice = June 21, 22 Winter solstice = December 21,22

B Spring 153 million km 147 million km Summer C A Winter D Fall

Fall 153 million km Winter Summer 147 million km Spring

22.2 Earth’s Moon

1. It takes 27 1/3 days for the moon to rotate once on its axis. 2. It takes 27 1/3 days for the moon to revolve once around Earth.

3. We always see the same side of the moon because it rotates and revolves at the same speed. 4. The moon shines by reflecting sunlight.

5. Waxing – when the lighted portion of the moon grows larger. 6. Waning – when the lighted portion of the moon becomes smaller.

7. It takes 29 ½ days for the moon to complete its cycle of phases.

9. The revolution of the moon and Earth causes eclipses. 10. There are 4/year. 2 solar and 2 lunar.

11. Solar eclipse – when the moon blocks the sun from the Earth.

12. Lunar eclipse – when the Earth blocks the sun from the moon.

Umbra – darkest portion of the Earth’s or moon’s shadow. A person standing in the umbra sees a total eclipse.

Penumbra – lighter portion of the Earth’s or moon’s shadow. A person standing in the penumbra sees a partial eclipse.

If you see a total lunar eclipse the moon is in the Earth’s umbra. If you see a partial lunar eclipse the moon is in the Earth’s penumbra.

15. Maria – dark regions of solidified lava, formed 3.2-3.8 billion years ago.

16. Copernicus and Tycho are craters caused by the impact of a meteor or an asteroid.

Copernicus

Tycho

3 main theories of how the moon formed: 1. Accretion – the moon condensed from loose material surrounding Earth as it was forming.

2. Capture – the moon formed elsewhere, wandered into Earth’s vicinity and was captured by Earth’s gravity

Impact – A Mars-sized object collided with Earth as it was forming Impact – A Mars-sized object collided with Earth as it was forming. The ejected debris condensed and formed the moon. The Impact Theory is the most widely accepted by scientists today.