Star Bright
Star Light, Star Bright. In this lesson the student will examine how a star’s distance and size affects its apparent magnitude.
The measure of a star’s brightness as it is seen from the Earth is known as magnitude. The higher the magnitude, the fainter the star. A star’s magnitude depends on three things---size, distance from Earth, and temperature. The larger the star is, the brighter the light that is seen on Earth. Stars have varying sizes. Some are smaller than the Earth. The Sun is considered a medium-sized star, with a diameter of 870,000 miles.
The light spreads out uniformly in all directions from stars. The spreading of light from more distant stars results in less light reaching Earth. Thus, two stars with the same luminosity, but at different distances from Earth, will appear to have different magnitudes. It is hard to know how far away stars are because we don’t know if one is really brighter than others, or just closer to us. This concept holds true for the flashlight demonstration in Part 2 of this exploration.
Materials Required:
· Two flashlights
· Aluminum foil
· Pencil
Procedure:
Part 1 - Size of a Star Exploration
1. Cover the top of one of the two flashlights with foil and punch a pencil-sized hole in the center
2. Dim the lights.
3. Shine both flashlights on the wall from the same point in the room.
4. Observe which star is brighter and which is dimmer.
Questions
· What can you say about the two stars you created with the flashlights?
· Why does one star appear brighter than the other?
Part 2 – Distance of a Star Exploration
1. Remove the aluminum foil from the flashlight.
2. Shine both flashlights on the wall from an equal distance away, and observe that both stars appear to be the same brightness.
3. Move one of the flashlights far away from the wall and the other very close. What do you notice?
4. The light from the flashlights represents the light from two stars that give off the same light. Which flashlight star looks brighter? Explain why one star appears brighter than the other.
Based on your observations using the flashlights, support an argument that the differences in the apparent brightness of the stars is because of their size and their distance from earth.