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The Question

(Submitted October 20, 1997)

I have a troop of Girls Scout ages 7, 8, 9, years old. In our Girl Scout book the girl have to learn what make the stars appear to be brighter or bigger than others, about the different colors that appear to the star. My husband knows some things about the stars and he is my co-leader but he doesn't know how to tell little girls about the stars without them walking way not knowing what he said. He need help telling it right to kids. Please help!

The Answer

I think what you are looking for is a familiar analogy, or something the troop can understand by experimenting.

There are two main reasons why one star could be brighter than another star. The first is that it produces MORE LIGHT. The second reason that a star can be brighter is if it is CLOSER to us. A good way to explain these two reasons to kids would be to compare the stars to light bulbs or flashlights. The scout leader can demonstrate using 2 light bulbs (say a 100 watt bulb and a 45 watt one), first putting them side by side, then moving the 45 watt bulb close and closer to the girls. Or the troop can gather in a darkened room (or go outside at night), each with her own flashlight (some are likely to be brighter than others), move about randomly and then guess who has the most powerful flashlight. They will be able to see for themselves that a dim flashlight right next to you can appear brighter than a powerful one further away.

Stars look different colors because they are different temperatures. Hotter stars are white or even blue and cooler stars are orange or red. The girls already have some experience with this but they just don't know it yet! Think about an electric stovetop. When it is turned on, the coils start to glow. At first they turn red, then orange and then brighter orange as they heat up. The center of a candle flame is even hotter than a stovetop (though it is a much smaller area, so it can't heat as much), and it is BLUE! The scout leader can show them a candle flame to demonstrate. It actually has different colors, all corresponding to different temperatures. The coolest parts are the ones near the outside (near the outside air) and the hottest parts are in the center of the flame.

By relating stars to this kind of down to earth examples, the girls should be able to come away with an understanding of what makes the stars look different; and better yet, the explanation will make sense, so hopefully it will stick!

Allie Cliffe and Koji Mukai
for Ask an Astrophysicist

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