Observations and results
Was the light on the paper much brighter when the book was vertically in front of the flashlight compared with 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 shined on the sheet of paper placed straight in front of it, the light formed a crisp, bright circle. When the book was tilted back 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). As the book is tilted away from the flashlight, the light rays hitting the paper's surface become more slanted. Slanted light rays are weaker because they cover a larger area and heat the air and surface less than direct rays do. The same thing happens with Earth and the sun. When Earth's North Pole is tilted toward the sun, the direct rays make the sunlight stronger and thereby warmer in North America—causing it to be summertime—compared with when the North Pole is tilted away from the sun. In that instance North America gets less direct rays and more slanted ones, causing it to be colder—what we know to be wintertime. The middle of the planet, the equator, never gets tilted too far from the sun, which is why most places closer to the equator, such as Florida, have seasons that are defined less by temperature change than do places farther away from the equator, such as Minneapolis.
More to explore
What causes the seasons?, from NASA
Moon May Save Earth from Chaotic Tilting of Other Planets, from John Noble Wilford, the New York Times
Fun, Science Activities for You and Your Family, from Science Buddies
The Reasons for the Seasons, from Science Buddies
This activity brought to you in partnership with Science Buddies