BACKGROUND:
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.
PROCEDURE:
- 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.
- 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.
- 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.
- 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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