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Activities to Compare the Size of the Sun & the Moon

Seeing the sun and the moon is a regular occurrence for most of us, making these two celestial bodies a suitable introduction to astronomy for younger students. The sun is 400 times bigger than the moon and 400 times as far away, which makes it appear from earth, as if the moon and sun are the same size. Students will soon discover this is not the case after performing some activities to determine the very different sizes of these two bodies. These activities are suitable for elementary to middle school students.

Eclipse
- Investigate how the tiny moon appears to completely hide the giant sun.
  
  During an eclipse the moon, with its diameter of 12,756 km, can hide the sun, which has a diameter of 1,377,648 km, from view. Use a basketball and a ping-pong ball to represent the sun and moon. Organize students into pairs and instruct one student to hold the ping-pong ball at arms length and the other student, holding the basketball to move away from him until the "moon" completely hides the "sun." This is a fascinating introduction for elementary school students, about how distance can alter the perceived size of an object.
Calculating Diameter
- You will need to perform this activity on a sunny day.
  
  Instruct students to cut a 3/4 inch by 3/4 inch square in the center of a piece of card. Tape a piece of tinfoil over the square and use a pin to make a tiny hole in the tinfoil. This is called a pin-hole viewer. Place a piece of paper on the table and adjust the pin-hole viewer so that sunlight passes through the hole, onto the paper. Students should measure the diameter of the image on the paper (A) and the distance from the hole to the paper (B). To calculate the diameter of the sun, multiply measurement A over measurement B by the distance from the earth to the sun, approximately 149,600,000 km. Elementary students may require extra help with the calculations.
Relative Sizes
- The sun is the biggest celestial body in our solar system.
  
  This activity is adapted from Home Training Tools Comet Project. Inform the students that the diameter of the sun is 400 times that of the moon (according to Free Mars.org.) Hand each student a pin. The pin head will represent the moon. Instruct students to find everyday objects around school or home to represent the sun. Students will have to make careful calculations to ensure each object that represents the sun is the correct size in relation to the pin head. They can also alter the size of the object that is used to represent the moon.
Making Models
- Hang the models from the ceiling, like this solar system model.
  
  Making papier mache models of the sun and the moon can be an interesting craft activity for students of all ages. The models can also be useful tools in the classroom for representing the relative sizes of these two celestial bodies. Use the largest balloons you can find as a mold for the papier mache, ensure they are blown up as big as they will go. When students have finished decorating their sun models, they should then carefully calculate the relative size of the moon, as in Section 3. The very small moon models will not require a balloon, they can simply be molded into shape.

Astronomy