1. Chapter 19.1 Earth in Space p. 660-665

2. The Past: At one time people thought the Earth was the center of the universe. They believed Earth stood still and the sun traveled around it. At one time people thought the Earth was the center of the universe. They believed Earth stood still and the sun traveled around it. Why would they think this? Why would they think this?Today: We know that the Sun appears to move across the sky because Earth is spinning as it travels around the sun. We know that the Sun appears to move across the sky because Earth is spinning as it travels around the sun. Understanding our Solar System

3. Earth’s Rotation Axis- the imaginary line around which the Earth spins. Rotation- the spinning of Earth on its axis. Rotation is what causes day and night. During daytime the Earth is rotating, and the sun appears to move across the sky. During daytime the Earth is rotating, and the sun appears to move across the sky. During the nighttime the Earth has spun away from the Sun, causing the sun to no longer be visible. During the nighttime the Earth has spun away from the Sun, causing the sun to no longer be visible.

4. Earth’s Rotation One complete rotation takes 24 hours, or one day. One complete rotation takes 24 hours, or one day. The Earth completes about 365 rotations during one year. The Earth completes about 365 rotations during one year. This is also the number of days it takes the Earth to revolve around the sun one time. This is also the number of days it takes the Earth to revolve around the sun one time.

5. Seasons Revolution- The orbiting of one object around another, like Earth’s yearly orbit around the sun. Revolution- The orbiting of one object around another, like Earth’s yearly orbit around the sun. The Earth’s revolution, or path around the sun, controls the seasons. We know that the Earth orbits the Sun in an elliptical path and it takes 365 days to do this.

6. Ellipse- Elongated, closed curve. It looks like an oval shaped curve. Ellipse- Elongated, closed curve. It looks like an oval shaped curve. Since the Earth travels on this oval shaped path, the Earth does not maintain the same distance from the sun at all times. Since the Earth travels on this oval shaped path, the Earth does not maintain the same distance from the sun at all times.

7. Revolution The Earth is closest to the Sun on January 3 rd and farthest on July 4 th. The Earth is closest to the Sun on January 3 rd and farthest on July 4 th. Is this elliptical orbit causing the changing temperatures on Earth? Is this elliptical orbit causing the changing temperatures on Earth? Not entirely. Not entirely. The Earth does not see major changes in the amount of energy it receives from the sun throughout the year. However, a particular place can receive more energy than other places. Why??? The Earth does not see major changes in the amount of energy it receives from the sun throughout the year. However, a particular place can receive more energy than other places. Why???

8. Earth’s Tilted Axis The Earth’s axis is 23.5 degrees from a line perpendicular to its axis. The tilt is what causes the seasons, not how near or far we are from the sun. The Earth’s axis is 23.5 degrees from a line perpendicular to its axis. The tilt is what causes the seasons, not how near or far we are from the sun. Daytime hours are longer when the Earth is tilted toward the Sun, and the Sun also strikes that part of the Earth at a higher angle. This causes the part of the Earth that is tilted toward the sun to receive more radiation per unit area than the hemisphere that is tilted away from the sun. Daytime hours are longer when the Earth is tilted toward the Sun, and the Sun also strikes that part of the Earth at a higher angle. This causes the part of the Earth that is tilted toward the sun to receive more radiation per unit area than the hemisphere that is tilted away from the sun.

9. Equinoxes and Solstices Because of the Earth’s tilt, the sun’s position relative to the equator is constantly changing. Most of the time it is either north or south of the equator. However, twice during the year, the sun is directly over the equator. Because of the Earth’s tilt, the sun’s position relative to the equator is constantly changing. Most of the time it is either north or south of the equator. However, twice during the year, the sun is directly over the equator. When the sun reaches an equinox, it is directly above the equator and the number of daylight hours is exactly equal to the number of night-time hours, all over the world. When the sun reaches an equinox, it is directly above the equator and the number of daylight hours is exactly equal to the number of night-time hours, all over the world.

10. Equinoxes Neither hemisphere is tilted toward the sun on those days. Neither hemisphere is tilted toward the sun on those days. In the Northern Hemisphere, the spring equinox is on March 20 or 21. The fall equinox falls on September 22 or 23. In the Northern Hemisphere, the spring equinox is on March 20 or 21. The fall equinox falls on September 22 or 23. In the Southern Hemisphere, the spring equinox occurs on September 22 or 23 and their fall equinox on March 20 or 21. In the Southern Hemisphere, the spring equinox occurs on September 22 or 23 and their fall equinox on March 20 or 21. *******Our Seasons are Opposite******* *******Our Seasons are Opposite*******

11. Solstice A solstice is the point at which the sun reaches its greatest distance north or south of the equator. A solstice is the point at which the sun reaches its greatest distance north or south of the equator. In the Northern hemisphere, the summer solstice is June 21 or 22, and the winter solstice is December 21 or 22. In the Northern hemisphere, the summer solstice is June 21 or 22, and the winter solstice is December 21 or 22. The opposite is true in the Southern Hemisphere. The summer solstice brings us the longest day, and the winter solstice brings us the shortest day. The opposite is true in the Southern Hemisphere. The summer solstice brings us the longest day, and the winter solstice brings us the shortest day.