Grade Level
7–12

National Standards Addressed
Grades 5–8:
Earth and Space Science: Earth in the Solar System
Science as Inquiry: Design and Conduct Investigation; Analyze and Interpret Data, Develop Explanations, Think Critically

Grades 9–12
Abilities Necessary to Do Scientific Inquiry

Key Concepts
Equator, earth's orbit around the sun, shadows, equinox, earth's axis

Background Science
"The Earth's Rotation"
From Harvard's Everyday Classroom Tools
http://hea-www.harvard.edu/ECT/the_book/Chap1/Chapter1.html

"For Every Season There Is a Reason"
From the Astronomical Society of the Pacific
http://www.astrosociety.org/education/publications/tnl/29/29.html

Media
Download the video clips in this Teacher Guide or watch the entire Webcast. (Right-click and choose "save link as" to download a video clip.)

Clip 1 - How the earth's tilted axis affects where sunlight strikes the earth
Clip 2 - Bending the paper clips
Clip 3 - Labeled locations on the basketball
Clip 4 - Shadow pointing due north
Clip 5 - Why do the shadows change over the year?

Flash animation: How does the area of the earth that is lit by the sun change as the year progresses?

Ideas for Discussion
• Imagine you're making a sundial (you can make one with the sun clock activity below). A sundial helps us tell time by marking the movement of a shadow as the day progresses. What effect do seasonal changes in shadows have on a sundial?

• In the activity "Knowing North" you can use a dial watch to determine which direction is north. What effect does the season have on the results of this activity?

Going Further
Make a sun clock and use a shadow to tell time
http://www.exploratorium.edu/science_explorer/sunclock.html

Check for Understanding
• What can your shadow tell you about what time of year it is? How is your shadow different in winter than in summer?

• If you lived at one of the earth's poles, when during the year would your shadow be longest? When would it be shortest?