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Your web browser (Safari 7) is out of date. For more security, comfort and the best experience on this site: Update your browser Ignore Activitydevelop Family Version THE REASO N FO R THE SEASO NS How does the sun cause Earth's seasons? OVERVIEW Use a piece of round fruit and a flashlight to investigate the sun's intensity on the surface of the Earth. For the complete activity with media resources, visit: http://www.nationalgeographic.org/activity/the-reason-for-the-seasons/ Program DIRECTIO NS 1. Think about why we have seasons. Do you know why there are seasons? It s because of the positions of the sun and the Earth. Look at the illustration "Seasons." You re going to do a hands-on activity to see how seasons work! 2. Gather your materials. Gather together all of the materials you ll need: an orange, two toothpicks, a flashlight, and a permanent marker. Make sure you have space to move, and a 1 of 6

family member to help. 3. Create your Earth. Stick one toothpick in the top of the orange. That toothpick is the North Pole. Stick the other toothpick in the bottom of the orange. That toothpick is the South Pole. Use the permanent marker to draw a line around the middle of the orange. That line is the Equator. Then draw a dot halfway between the line and the top toothpick. The dot is a person living in the Northern Hemisphere, the part of the Earth that is north of the Equator. In this activity, imagine you live where the dot appears. 4. Investigate summer sunlight. Now turn on the flashlight and turn off the lights. Have your family member hold the Earth for you. Shine the flashlight straight at the middle line, or Equator. Ask your family member to tilt the North Pole toothpick toward the light. Where does most of the light shine? On the dot and the top half of the orange. This is the position of the Earth in summer. How much daylight does the North Pole receive as the Earth rotates on its axis? It is daylight 24 hours during this season. How much sun does the South Pole receive? None. It is dark until spring. 5. Investigate winter sunlight. Next, ask your family member to tilt the North Pole away from the light. Where does most of the light shine? It should shine on the bottom half of the orange. This is the Southern Hemisphere, the part of the Earth that is south of the Equator. This is the position of the Earth in winter. How much daylight does the North Pole receive as the Earth rotates on its axis? None. It is dark until spring. How much sun does the South Pole receive? It is daylight 24 hours during this season. 6. Investigate sunlight at the Equator. Have you noticed how much light shines on the middle? The amount of light stays about the same all year round at the Equator. That means the days stay warm and about the same length all year long. 2 of 6

Quiz Yourself! Why are there seasons? There are seasons because of the position of Earth in its rotation around the sun. WHAT YOU LL NEED MATERIA LS YO U PRO V IDE Black construction paper Flashlights Globe Markers Polystyrene foam balls or round fruit Push pins Rulers Scissors Toothpicks Transparent tape REQ UIRED TECH N O LO GY Internet Access: Optional Tech Setup: 1 computer per classroom, Projector, Speakers Plug-Ins: Flash RECOMMEN DED PRIO R A CTIV ITIES None 3 of 6

RES O URCES PRO V IDED: IMA GES Seasons BACKGROUND Background Information The changing position of the Earth s tilt is the reason for the differences in temperature and length of daylight that distinguish the seasons. When the Northern Hemisphere of the Earth is leaning toward the sun, it receives direct sunlight. The warmth of direct rays causes spring and then summer in that part of the globe. When the Northern Hemisphere of the Earth is leaning away from the sun, it receives more indirect sunlight. The cooling effects of more indirect sunlight cause autumn and winter. Because of the Earth s approximately 23.5º tilt, the seasons in the Northern and Southern Hemispheres are reversed, about six months apart from each other. Vocabulary Term Part of Speech acute angle angle autumnal equinox 4 of 6 Definition angle measuring between 0 and 90 degrees. slanting space between two lines that ultimately meet in a point. autumn day, usually around September 22, when day and night are of generally equal length. axis an invisible line around which an object spins. Equator hemisphere Northern Hemisphere imaginary line around the Earth, another planet, or star running east-west, 0 degrees latitude. half of a sphere, or ball-shaped object. half of the Earth between the North Pole and the Equator.

North Pole obtuse angle fixed point that, along with the South Pole, forms the axis on which the Earth spins. angle measuring more than 90 degrees, but less than 180 degrees. orbit path of one object around a more massive object. season solar radiation Southern Hemisphere South Pole summer solstice temperature period of the year distinguished by special climatic conditions. light and heat from the sun. half of the Earth between the South Pole and the Equator. fixed point that, along with the North Pole, forms the axis on which the Earth spins. day of the year with the most hours of sunlight, June 20 or 21 in the Northern Hemisphere and December 21 or 22 in the Southern Hemisphere. degree of hotness or coldness measured by a thermometer with a numerical scale. tilt verb to lean or slant. vernal Term equinox winter solstice Part of Speech day, usually around March 21, when day and night are of generally equal length. Also called the spring equinox. (December 22 in the Northern Hemisphere, June 22 in the Southern Hemisphere) longest night of the year and the beginning of winter. LEARN MORE For Further Exploration Definition Websites NASA: Educator Features Planetary Seasons 5 of 6