Date: Sunday, March 11^th, 2018

Lesson 1:  What Causes Earth’s Seasons?

VOCABULARY

Axis: This imaginary line through Earth is called Earth’s axis.

Rotation: The spinning of Earth on its axis is called rotation.

Revolution: One trip around the sun is one revolution.

How Earth Moves

As you read this book, it may seem as if you’re sitting still. In fact, you’re moving through space at about 107,000 kilometers (about 66,000 mi) per hour! Although you don’t feel the motion, Earth is both traveling and spinning.

Earth spins just the way a top does. Picture a line going through Earth from the North Pole to the South Pole. This imaginary line through Earth is called Earth’s axis. Look at the picture on this page. As you can see, Earth’s axis is not straight up and down. Instead, the axis is tilted a little. The spinning of Earth on its axis is called rotation.

Rotation isn’t the only way Earth moves. Earth also revolves around the sun. One trip around the sun is one revolution. Each revolution takes about 365 days. People use Earth’s movements to measure time. One rotation of Earth takes one day. One revolution of Earth takes one year.

MAIN IDEA AND DETAILS What are the two ways in which Earth moves? Seasons During the year, some parts of Earth have four seasons—winter, spring, summer, and fall—with different weather. One weather difference is temperature. You might wonder what causes these temperature differences. In the Investigate, you learned that when light rays strike directly, the light is brighter than when they strike at a slant. That’s because light rays that strike at a slant spread out more.

Earth is tilted on its axis as it revolves. This causes the same part of Earth that is tilted toward the sun at one time to be tilted away from it at another. Places, where the sun’s rays strike directly, are warmer than places where the rays strike at a slant.

Where the sun’s rays strike Earth directly, the season is summer. Where they strike Earth at the greatest slant, the season is winter.

MAIN IDEA AND DETAILS   what causes seasons?

Day and Night

Earth takes one year to revolve around the sun, but only one day to rotate. As it rotates, half of Earth faces the sun and has daytime. The other half of Earth faces away from the sun and has nighttime.

Since some places have day while others have night, it can’t be the same time everywhere. People have divided the world into time zones so that places near one another have the same time. When it’s 12 noon in Orlando Florida, its 6 o’clock in the evening in Madrid, Spain.

MAIN IDEA AND DETAILS What causes day and night?