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Let the Sun Shine In!


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  • When the summer approaches, the weather gets warmer, and the most important thing on most kids' minds is vacation! This challenge has to do with why it gets warmer during the summer. Many people think it's because Earth is closer to the Sun. In fact, this is only true if you live south of the equator. The distance between Earth and the Sun does change during the year, but perihelion, the point in our orbit where we're closest to the Sun, happens on January 2nd! Since that's the middle of the winter for those of us in the northern hemisphere, there's got to be another explanation! Obviously, the Sun is what keeps us warm. But how does it affect temperature change here on Earth? If you're a careful observer and you have about two weeks to wait, you can discover the reason for the seasons yourself.

    Here's what you'll need to play along:

    • a piece of graph paper
    • a pencil
    • an accurate clock
    • a meter stick
    • a tape measure
    To begin, find a clear open space where the sun shines down. (Stay away from buildings or trees that might cast a shadow.) A schoolyard or an open field works best. Then get your piece of graph paper and make a chart with three columns. Mark the first column "date," the second column "length of shadow," and the third column "time."

    You may also want to review our The Shadow Knows investigation on shadow and light before you tackle this challenge.

    Here's the challenge question:

    What does the position of the Sun in the sky have to do with the seasons on Earth?

    What you do:

    First, think about what you already know about how the Sun appears to move across the sky, and what happens to the length of daylight as the seasons change. Then, predict what you think the answer to the challenge question will be.

    On the first day of your investigation, place one end of the meter stick on the ground and hold it so it is straight up and down. Use the tape measure to measure how long the shadow is. Record it on your chart along with the time and date. Try to be as precise as possible on your measurement.

    Now here's the tricky part: You must go out each day for the next two weeks at the exact same time in the same location and repeat the experiment. (If you're doing this at home, try to do it right before you go to school or as soon as you get home.) If it rains or if it's too cloudy to see the shadow, note it on your chart. Chances are, within the two-week period you'll have enough sunny days to collect the data you need. As soon as you see a pattern appear in your chart, check your prediction and try to interpret your results! Good luck and may sunny days be yours!

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    Notes to Teachers

    Learning Outcomes:

    Use the scientific processes of measurement and record keeping.

    Draw conclusions based on scientific observation.

    Discover the relationship between shadows, the position of the sun, and seasonal change.

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    Web Links

    Try these sites for more information and activities about the Sun:

    Sundials
    http://cpcug.org/user/jaubert/jsundial.html

    Here you will find complete technical details, drawings, history, and explanations for building a sundial that works. Topics covered include placement, construction, finding true north, adjusting for clock time, the seasons, and more.

    About the Sun
    http://www.hao.ucar.edu/public/education/education.html

    The National Science Foundation's High Altitude Observatory provides a basic introduction to Earth's most important star -- the Sun.

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