How The Earth Turns
By: Margaret M. Ulrich-Urban
Adapted from the text:
"Project Earth Science: Astronomy"
By: P.Sean Smith
Acknowledgements
This electronic book is dedicated to Lauren Johnson who is a wonderful person, who enjoys reading, and has the capability and intellect to learn the many fascinating things about the world we live in.
The Earth sits on its axis. You can think of the Earth's axis as an imaginary line that goes through the Earth. The neat thing about this axis is that it is slanted or tilts on an angle.
The Earth rotates or spins on its axis every 24 hours. This is why we have day and night. The Earth makes one complete rotation on its axis everyday.
The Earth revolves around the sun. It follows a special path called an orbit . The orbit that the Earth is following is a slightly elliptical orbit . It is so slight, that it looks almost round. It takes 365 days or 1 year for the Earth to follow this orbit around the sun.
While the Earth is rotating on its axis , it is revolving around the sun.
Below is a link to a video clip of the Earth revolving around the Sun. Notice how the Earth is rotating or spinning as the Earth is revolving around the Sun. Take a careful look at the elliptical orbit the Earth is following around the Sun.
www.classzone.com/books/earth_science/terc/content/visualizations/es0408/es0408page01.cfm
The Hemispheres
The Earth is divided into four hemispheres . The Northern Hemisphere is the top half of the Earth. The Southern Hemisphere is the bottom half of the Earth. The Western Hemisphere is the left side of the Earth, and the Eastern Hemisphere is the right side of the Earth.
The reason we have seasons is because the Earth sits on its axis . Depending on which hemisphere faces the sun determines what season it is.
When a hemisphere is tilted toward the Sun, it is summer time. When a hemisphere is tilted away from the Sun it is winter time.
Look at the picture above. Notice that when it is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere and when it is Spring in the Northern Hemisphere it is Autumn in the Southern Hemisphere. I guess you could think of the seasons as opposites. Summer is the opposite of Winter, and Spring is the opposite of Autumn. When one season happens in the Northern Hemisphere, the opposite season happens in the Southern Hemisphere.
Answer Key
1. What season is it in the Northern Hemisphere when it is facing the sun?
2. How many days does it take the Earth to revolve around the Sun?
3. How often does the Earth rotate?