Universe Cycle - Universe (K)

  • Comparing sizes and distances in space.
  • Discovering that stars are far away.
  • absolute brightness
  • relative brightness
  • star
  • space
  • Universe
  • Styrofoam balls (different sizes)

Students try to find the largest star.

The brighter the star does not mean it is closest. 


The night sky is full of points of light. It is difficult to tell if one light corresponds to a small star that is close to the Earth or a large star that is far away. A point of light could also be an entire galaxy!

The real or "absolute brightness" of stars depends on their size and the types of fuel they are burning. Our eyes are not able to detect the absolute brightness of stars. Instead, we see "relative" brightness, which depends on how close a star is to Earth. A nearby star appears brighter than a faraway star, even if the absolute brightness of the faraway star is greater.

  1. Introduce "absolute" and "relative" brightness to your students. Make sure you repeat the terms and their definitions over and over. Here are simple ways to define absolute and relative brightness:

    Absolute means that if all the stars were put at the same distance, some would be brighter than others, because some are larger or give off more radiation.

    Relative means the brightness as our eyes see the object from the Earth. A star that is bigger, but farther away, will not shine as bright to our eyes.

  2. Discuss how far the stars are from Earth. Ask students if the Moon is closer than the stars. You may want to show students a picture of the night sky showing the Moon and stars. Then ask them which objects look bigger. Most of the children will say the Moon is larger. However, tell them that the stars are larger, much larger, but they are just far, far away. Tell them you will be proving this to them during this activity.
  3. In this lab, give each child a styrofoam ball, make sure there is at least one ball that is larger than all the rest. You may want them to paint the balls yellow, red, blue, or orange to represent stars. Go outside and position the students at different distances from one central point "A." All students will rotate around this central point. Use a "star" or circle figure which represents the person at point "A". You may want have two students in the front. Make sure the smallest balls are closer to point "A" and the larger ball is further away.
  4. Tell students that they should make-believe they are stars in the sky. Each child should have a chance to be at point "A." Ask the students to try and find the largest ball. After they have tried to find the largest "star," discuss with the children that the distance of stars plays an important part on how we see things with our eyes. Sometimes what we see is not how it really is!

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