Seasonal Science: The Reasons for the Seasons
Have you ever lived someplace where you get to experience the full glory of all four seasons? If so, you know well the heady blossoms and dramatic skies of spring; the long, sun-drenched days of summer; the trees shaking in crimson and gold in fall; and the sparkling, brittle snows of winter. But do you know why we have these seasons, over and over again, in a cycle as predictable as the rising and setting of the sun? It actually has to do with the Earth’s tilt and the Moon. In this science activity, you’ll investigate how the Earth’s tilt affects how the Sun’s rays strike the Earth and create seasons.
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
Where most people live on Earth, in the Northern hemisphere, summers are hot and filled with many hours of strong sunlight, while winters are cold due to shortened hours of daylight and weak sunlight. Why is this? One big part of the answer is that Earth is tilted on its axis. To visualize the Earth’s axis, picture an imaginary stick going through the North and South poles of Earth. Earth does a complete rotation about this axis every 24 hours.
However, this axis isn’t straight up and down as Earth goes through its orbit about the Sun. Instead, the axis is tilted by approximately 23 degrees. Earth’s axis remains fixed in space, always pointing in the same direction, as Earth goes through its orbit around the Sun, and the tilt changes how the sunlight hits Earth at a given location. When it is summer in North America, the top part of the axis (the North pole) points in the direction of the Sun, and the Sun’s rays shine directly on North America; while in South America, where it’s winter, the axis is tipped away from the Sun and the Sun’s rays hit Earth on a slant.
Extra: Repeat this activity using a larger range of degrees, such as 20, 30, 40, etc. You will want to do this using a protractor at the base of the book as you tilt it. How does the light outline change as you increase the angle of the book?
Extra: Try repeating this activity but instead of a blank sheet of paper use graph paper. When you are done making your outlines, you can count how many squares are filled by light when the book isn’t tilted compared to when it’s at a 45 degree angle. Using these numbers, just how different are the two outlines in size?
Extra: You could repeat this activity using a light meter, which would let you quantify your brightness observations. Just how much brighter is the light on the paper at one angle compared to another angle?
Observations and Results
Was the light on the paper much brighter when the book was vertically in front of the flashlight compared to when the book was at a 45 degree angle away from the flashlight? Did the outline get bigger and elongated when the book was tilted away from the flashlight?
In this activity you should have seen that when the flashlight was shown on the sheet of paper placed vertically in front of it, the light formed a crisp, bright circle. When the book was tilted back by 45 degrees, away from the flashlight, it should have made an oval shape that was much dimmer and larger (almost twice the size of the first outline). Basically, as the book is being tilted away from the flashlight, the light rays that hit the paper’s surface become more slanted. Slanted light rays are weaker rays because they cover a larger area and heat the air and surface less than direct rays do. The same thing happens with the Earth and Sun. When Earth’s North Pole is tilted towards the Sun, the direct rays make it generally warmer and sunnier in North America – causing it to be summer time – compared to when the North Pole is tilted away from the Sun (then North America gets less direct rays and more slanted ones, causing it to be winter time).
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Teisha Rowland, PhD, Science Buddies
Science Buddies |
The Sun, light, the seasons, Earth’s orbit
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