1. How Does Earth’s Orbit Affect the Seasons?
Intro to Night & Day
How Does Earth’s Orbit Affect the Seasons?

2. Fast Fact
Sunrise from Space – Astronauts in space may see 16 sunrises and 16 sunsets everyday as they travel around Earth. In the Investigate, you’ll learn about movements of Earth and the moon and why, here on Earth, we see only 1 sunrise and 1 sunset each day.

3. Day and Night
Every day the sun appears to rise in the east. It appears to reach its highest point around noon , and set in the west. After a period of darkness, this process repeats itself.

4. Can You Explain It? Does the sun really rise and set?
No, it is the rotation of Earth that causes the appearance of a sunrise and sunset.

5. Explain It
This cycle of day and night occurs because Earth rotates, or spins on its axis. When a place on Earth faces the sun, it is day in that place. When that place faces away from the sun, it is night.

6. Definitions You Need to Know
Sun – the star at the center of our solar system.
Rotate – to spin on an axis.
Axis – an imaginary line that passes through the North and South Poles.

7. Standard Times
Our system of time is based on Earth’s 24 hour cycle of daylight and darkness.
Because of Earth’s rotation, sunrise and sunset occur at different times for different places.

8. Time Zones
If we had one single time zone for Earth, noon would be the middle of the day in some places, but it would be morning, evening, and the middle of the night in others. Since different parts of Earth enter and exit daylight at different times, we need different time zones.

9. Trains Made a Difference
Starting in the 1800’s, the invention of the train made it possible for people to travel from one time zone to another.
To avoid confusion, standard times were developed.

10. Quick Review - Main Idea
Explain why officials needed to set up time zones in the late 1800’s.
People needed standard times to avoid confusion after they began to travel long distances on trains.

11. Insta-Lab
Sunrise, Sunset Demonstration – Use a flashlight and a ball to model day and night.
Where on the ball are sunrise and sunset represented?

12. Why Does Earth Have Seasons?
Earth’s axis is tilted which causes the hemisphere that is tilted toward the Sun to experience summer. The days are longer and the temperature is warmer.
The hemisphere that is tilted away from the Sun will experience winter. The days will be shorter and the temperatures will be colder.

13. Seasons – Tilt Demonstration
Tilt the North Pole toward the sun, with North America on the sun side. This is our summer.
As the globe turns counterclockwise it becomes fall in North America. The days are shorter and it is not as warm.
As the globe continues to slide counterclockwise to the winter solstice, it is winter in North America.

14. Critical Thinking
When it is summer in the Northern Hemisphere, what season is it in the Southern Hemisphere? Explain why.
It would be winter because the South Pole is tilted away from the Sun
Why is it warmer in the summer than in the winter?
Because Earth is tilted toward the Sun so it gets more heat energy.

15. More Vocabulary Revolve – to travel in a path around another object.
Orbit – the path that Earth takes as it moves around the sun.
Equator – the imaginary line that divides Earth into the Northern and Southern Hemispheres.