Unit D: Patterns in the Sky

Why doesn't it snow everywhere in winter?

1. Get Set to Explore


  • average: Number found by dividing the sum of two or more quantities by the number of quantities.
  • temperature: Measure of heat or cold.
  • axis: An imaginary line that passes through Earth from the North Pole to the South Pole.

Building Background

  • Show children a globe and guide them to note how the globe is tilted to show the tilt of Earth. Earth's axis is tilted at 23.5 degrees from the vertical. Review the definition of axis.
  • Use the globe to demonstrate how Earth revolves around the Sun. You may wish to use a standing lamp without a shade to represent the Sun. You can walk around the lamp and stop at different positions to show how the northern part of Earth sometimes tilts toward the Sun and sometimes tilts away from the Sun. Explain that when our part of Earth is tilted toward the Sun, we have summer; when our part of Earth is tilted away from the Sun, we have winter.
  • Show children the equator. Explain that the equator goes around the exact middle of the globe. Make sure children understand that sometimes people use the word middle to describe the region around the equator.
  • Let volunteers find Boston, Massachusetts, and Miami, Florida, on the globe. Ask the class to note which city is closer to the equator—to Earth's middle region.
  • Review the vocabulary words and definitions with the class. Then introduce the Discover! question and let children predict the answer. Write their predictions on the board.

2. Guide the Exploration

  • Direct children to launch the Discover! Simulation. They should listen closely to the question and the directions.
  • Children should spend some time watching the movement of Earth around the Sun. Explain that when the picture of Earth stops, children should note several things: which part of Earth is tilted toward the Sun; whether either of the two cities has snow, as shown in the photos; the average monthly temperature in the two cities, as indicated by the caption below the photo.

3. Review/Assess

  • Then review Step 3's Wrap-Up text with the class. Reinforce the idea that Miami is farther south, and thus closer to the equator—the middle region of Earth—than Boston is. Explain that since the Sun is fairly high in the sky during the winter in Miami, the city gets strong sunlight and enough heat generally to prevent snow.
  • Pose the Extension question to the children: Is winter weather where you live more like winter in Miami or winter in Boston? If shown on the globe, let children find your city or your state on the globe and compare its location to those of Boston and Miami. Children should rank the three locations north to south. Guide them to use this information to notice patterns in winter weather in these places.
  • Apply this information or other information to answer the Extension question:
    • Places that are the same latitude or close to the same latitude as Boston have similar temperatures to those of Boston; it may snow there.
    • Places that are the same latitude or close to the same latitude as Miami have similar temperatures to those of Miami; it is unlikely to snow there.

If time permits, present children with the following questions:

  • Inquiry Skill Use Numbers Compare the average monthly temperatures for Boston and Miami. In which season do Boston and Miami have the closest average temperatures? Answer: Summer.
  • Critical Thinking Analyze Water freezes at 32°F. How does this fact help explain why Miami does not get snow and Boston gets snow only in the winter? Answer: Snow only forms when temperatures are at or below freezing. The average monthly temperature in Miami in all four seasons is above 32°F. In Boston, the average monthly temperature dips below 32°F only in winter.

4. Reaching All Learners

English Language Learners

To help English Language Learners practice English speaking and listening skills in a natural context, pair these children with native English speakers. Have native English speakers ask English learners about the weather in their home country. English Language Learners should talk about how warm or cold it is during different seasons and whether there is a lot of rain or snow. If English learners have not lived in or visited the place where their family came from, provide simple books and Internet resources so that the paired students can work together to learn about the weather in that place.