1. DAY AND NIGHT ON PLANET EARTH: TIME ZONES AND WHY WE HAVE THEM
Photos by Astronaut Sunita Williams
Text by Mrs. Birtwell

2. Why do we have time zones?
We have time zones because the Earth is constantly rotating east to west. Every 24 hours Earth experiences day and night. This is why there are 24 time zones on Earth!

3. Since parts of the Earth are in the sunlight before other parts at local dawn, those time zones are “ahead” of others.
Because the U.S. East Coast experiences sunrise and sunset before the rest of the U.S., our time is AHEAD of the rest of the continental U.S. time zones.

4. This picture shows day and night on Europe and Africa
This picture shows day and night on Europe and Africa. The Earth is turning to your right.

5. It is night in Europe and Africa.

10. On the next slide, you will see a satellite photo of Europe and Africa at night on a cloudless day.
Lights are already on in Paris but not in London, where there is still daylight.

11. Atlantic Ocean Canary Islands ÁFRICA Continental Platform England
Iceland
Atlantic
Ocean
France
Islas de la Madera y Azores
Spain
Italy
Already night time here.
Canary Islands
ÁFRICA
Cabo Verde Island

12. NIGHTFALL IN BRAZIL Atlantic Ocean Brazilian Continental Platform.
Belo Horizonte
Salvador
Rio de Janeiro
Grande São Paulo

13. THE U.S. TIME ZONES
There are four time zones in the continental United States.
The East Coast (whose time is ahead of the rest of the country) has EASTERN TIME.

14. The Midwest has CENTRAL TIME. It is ONE HOUR behind us.

15. The Rocky Mountain and desert states have MOUNTAIN TIME
The Rocky Mountain and desert states have MOUNTAIN TIME. It is TWO HOURS behind us.

16. The West Coast has PACIFIC TIME. It is THREE HOURS behind us.

17. See it for yourself!
In the next slide, you will see the real reason for having four time zones in the U.S.!
You will see that it is NIGHT on the East Coast, the Midwest, and part of the Mountain and desert states.
It is still daylight on the West Coast!
That is why when it is 9 PM in Boston, it is only 6 PM on the West Coast.

18. NIGHTFALL IN USA

19. Still daylight in California.
Chicago
The biggest concentration of lights (from top to bottom) are the cities of Boston, New York, Philadelphia and Washington.
Dallas
Puerto Rico
Houston
Miami

20. Extra added feature!! Coming up next is an actual photograph of sunset on MARS! This was taken by one of our Mars robots currently exploring the planet. Of course, there are no time zones on Mars –

22. By looking at these wonderful photos of Earth from space, it’s easy to understand why we have time zones!
THE END