Seasons Notes 10/12/18 Key Points: Earth’s Rotation Earth’s Revolution Motion Terminology Why Do We Have Seasons? Summer vs. Winter Solstices Equinoxes

Seasons Launch Lab Overview (Answer to the Intro Question)

1. Earth’s Rotation The Earth rotates on its axis every 23 hours & 56 minutes.

1. Earth’s Rotation B. One day on Earth is one rotation of the Earth. 1. One Day on Earth is when our side of the Earth faces the sun. 2. Night on Earth is when the side of Earth we are on faces away from the sun.

2. Earth’s Revolution It takes the Earth 365.25 days to travel or revolve around the Sun once. B. This is called a year.

3. Motion Terminology Rotation – to spin on an axis Revolution – the motion of a body around another body

3. Motion Terminology C. Orbit – the path that is followed around another body in space

3. Motion Terminology C. Orbit- the path that is followed around another body in space. 1. The Earth’s orbit around the sun is not a perfect circle. 2. The Earth’s orbit around the sun has the shape of an ellipse. Wrong! Ellipse

4. Why Do We Have Seasons? Seasons are not caused by how close the Earth is to the sun.

4. Why Do We Have Seasons? B. Seasons are the result of the tilt of the Earth's axis. 1. Earth’s axis is tilted 23.5°. 2. This tilting is why we have SEASONS like fall, winter, spring, summer.

5. Summer vs. Winter During Summer, Earth is tilted toward the Sun. 1. The summer is warmer than winter because the Sun's rays hit the Earth at a more direct angle during summer than during winter. 2. The days are much longer than the nights during the summer.

5. Summer vs. Winter B. During the winter, the Earth is tilting away from the Sun. 1. The Sun's rays hit the Earth at an extreme indirect angle. 2. The days during the winter are very short.

6. Solstices Occur twice a year

6. Solstices B. Solstices occur when the Earth's is tilted the farthest from the Sun during the Winter and closest to the Sun during the Summer

6. Solstices B. Solstices occur when the Earth's is tilted the farthest from the Sun during the Winter and closest to the Sun during the Summer 1. Winter solstice is the shortest day of the year. It occurs on December 21 or 22 and marks the beginning of winter. 2. Summer Solstice is the longest day of the year. It occurs on June 20 or 21 and marks the beginning of summer.

7. Equinoxes A. Equinox literally means "equal night". B. During an Equinox, a day lasts exactly 12 hours and a night lasts exactly 12 hours at all locations. C. Sunlight strikes the earth most directly at the equator during an equinox.

7. Equinoxes D. Occur twice a year 1. The vernal (Spring) equinox occurs March 20. 2. The autumnal (Fall) equinox occurs September 22 or 23.