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

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!

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.

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.

It is night in Europe and Africa.

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.

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

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

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.

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

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

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

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.

NIGHTFALL IN USA

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

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 –

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