Paper Plate Education
"Serving the Universe on a Paper Plate"

Activity: Seasons

The following text is excerpted from GLPA Proceedings, 1992, p. 83-84. Used with permission:

Objective: Build a paper plate model to help explain the cause of the seasons.

Materials: 2 paper plates per student

pencil

scissors

light bulb (unfrosted is best)

paper

Assessment: Have the student describe the seasons on other planets with different axis tilt than the earth.

Background: The cause of the seasons is due to the angle of the sunlight striking the ground. When the sun is high overhead, the light is more concentrated (summer) and when the sun is low the light is more spread out (winter). Measuring the sun's height at mid-day (See Altitude of Noon Sun or Altitude of Noon Sun II.) is a good exercise to prepare for this lesson. Most students think the sun is closer in summer and farther away in winter. The orbit of the earth is not a perfect circle, but the earth is closest in January. The sun is lowest for us in the northern hemisphere in mid to late December. The "lag-time" between the low sun and the coldest temperatures in January, is caused by the time it takes for the earth to cool off, just like the hottest time of day is late afternoon, not noon when the sun is highest (and the coldest daily temperature is many times after sunrise!)

The cause of the sun being at different mid-day heights during the year is the tilt of the earth's axis. If the earth did not have tilt, there would be no seasons. To explain this to students, use the extreme. Show the earth with no tilt, then with 90 degrees of tilt, then with 23.5 degrees tilt as it really is. Most errors are made when students are moving the 'earth' around the 'sun', they want to point the axis toward the sun and keep it toward the sun as it orbits (when showing 90 degrees tilt). This is why it is important to imagine a distant star much farther away than the sun to which the earth always is pointed. For scale, Polaris is 820 light YEARS away while the sun is 8.5 light MINUTES away.

"First use 2 plates to make a paper plate sphere (See exercise below or variation shown in Core of the Matter). Label the sphere with a north pole, south pole and equator. Pretend the earth were not tilted. The equator would then always be toward the sun (maximum heat due to the sun's energy coming straight down to the ground). The poles would always be in twilight with the light coming from the horizon. If you have trouble seeing this, cut out a small circle of paper (about the size of a penny). Pretend you are standing in the middle of it and the edges are your horizon. Place it at the equator and then at the poles. Look at the light from the bulb hitting the paper.

"Now pretend the sphere is tilted over 90 degrees. As it moves around the sun, first one pole would be pointing toward the sun, then the equator, then the other pole, then the equator, and finally the first pole again. Think about what the seasons would be like standing at different points on the sphere."

"The Earth is tilted over 23.5 degrees from the first exercise. You can estimate this by thinking about half of 90 is 45, half of 45 is 22.5, which is within one degree of the way Earth is tilted. Place your little circle of paper at different points on your sphere and describe the seasons."

Actual tilt of the objects in our solar system:

Mercury 0.0 degrees

Venus 177.0 degrees making it spin backwards

Earth 23.4 degrees

Moon 6.7 degrees

Mars 25.2 degrees

Jupiter 3.2 degrees

Saturn 26.7 degrees

Uranus 97.9 degrees similar to activity

Neptune 28.8 degrees

Pluto 94 degrees similar to Uranus

Paper Plate Exercise: MAKING A SPHERE

You will need at least three paper plates and scissors. You may want to use more plates depending on the degree of detail you want in your sphere.

Stack two plates and cut to the center from the edge. This edge becomes the end. (Fold in 4ths first if you want a line to follow and identify the center.) Turn one plate half way around so the slots face each other. Put them together and hold them so it makes an "X" when you look at them from the end. The ends become the poles of the spheres. Half way between the poles is the equator. Mark the point on one plate and cut half way to the center. Cut the third plate in half. Start from the center and cut half way to the edge. Place this 3rd plate slot to the slot marked for the sphere's equator and slide them together. Label your sphere. Mark one end "north", the opposite end "south", between them the "equator". The outer edge of the plate making the equator can represent a latitude line and trying to add other latitude lines north and/or south of this will show students you need a smaller plate as you get near the poles until the latitude line becomes a dot at the poles. The edge of the plates running from pole to pole represent the longitude lines. You would use full size plates to add more lines and see they would be farther apart near the equator and closer together near the poles. The sphere can represent a planet such as earth or any of the other planets. The sphere can also represent the sky if you pretend the earth is a dot at the center of the sphere and then the latitude lines become declination lines and the longitude lines become right ascension lines. If you add several plates and then cover the sphere with papermaché, you could have students draw surface detail for any of the planets being studied, or draw stars for the celestial sphere appearing to surround us in space.

Contributed by Wayne James.

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