Chapter 5 Lesson 2 “Earth and the Sun”

How Do We Know Earth is Rotating? The Sun only seems to move because the Earth is rotating or spinning.

Earth rotates on its axis. The axis is an imaginary line through Earth from the North Pole to the South Pole.

It takes about 24 hours for the Earth to make one rotation.

As a result of this motion, any location on Earth experiences a cycle of day and night.

Satellites can observe the rotation of Earth from space.

Due to its rotation, Earth is slightly flattened at the North and South Poles and bulges at the equator.

The sun rises in the east. The Sun reaches its highest point in the sky at noon.

What Are Standard Time Zones? You can use the rotation of Earth to measure the passage of time. Earth rotates 360 in 24 hours.

A standard time zone is a belt 15 degrees wide in longitude, in which all the places have the same time.

If you travel west, you must turn your clock back one hour for each time zone you cross. If you travel east, you must turn your clock ahead one hour for each time zone you cross.

The International Date Line was created as the location where a new day begins. The International Date line is the 180 degrees line of longitude. If you cross the International Date Line going west, you add a day.

Why Are There Seasons? Earth takes 365 ¼ days to revolve, or travel around the Sun. One complete trip around the Sun is called a revolution.

Earth’s axis is tilted at a 23 ½ degree angle.

The revolution of the tilted Earth around the Sun causes the seasons. When the Northern Hemisphere is tipped toward the Sun, that part of Earth is in the season called summer.

Where Is the Sun in Summer and Winter? In the summer, incoming rays from the Sun hit Earth at higher angles. In the winter the Sun’s rays are slanted at lower angles.

In the spring and fall, the angles of rays are somewhere in between. During the day you are on the side of Earth facing the Sun. At the same time, Earth’s opposite side is facing away from the Sun, experiencing night.

How Is the Sun an Important Energy Source? The Sun is the energy source for life on Earth.

Light from the Sun is necessary for the growth of most organisms. Plants and other producers trap the Sun’s energy and use it in their food-making process.

Fossil fuels that we use today were formed over time from the decay of ancient living things. The energy was stored in the fuels that formed over time.

The Sun is the source of energy for the water cycle.

The Sun’s energy causes ocean water to evaporate. As evaporated water rises, it forms clouds. These may bring rain or snow. The water may fall into oceans, rivers, and lakes.