The Backpacking Group's Light Test
On a backpacking trip, a group stops at Cedar Bowl Camp. After unpacking, the campers prepare prediction cards for an evening science discussion. One card asks why the Sun looks brighter than the other stars seen from Earth. The group gathers space information and plans a safe model investigation. They use an LED lamp instead of observing the Sun directly. Do not look directly at the Sun.
Their space information says that the Sun is a star that gives off its own light. Other stars also give off their own light. Stars differ in the amount of light they produce, and some produce more light than the Sun. The Sun is about 150 million kilometers from Earth. Even the nearest other star is about 40 trillion kilometers away. A trillion is a million millions.
For their model, the campers place a light meter on a stand on level ground. Its sensor measures the light reaching it from the lamp. They leave the meter in one place and move the same lamp to marks 1 meter, 2 meters, and 4 meters away. They keep the lamp's power setting, its height, and its direction toward the sensor the same. They also keep other lighting conditions the same.
At each mark, the campers record the meter's brightness reading. A larger reading means more lamp light reaches the sensor. The graph shows their model data in the meter's brightness units. These units are useful for comparing their trials; they are not measurements of stars. The campers do not change the power setting to make the readings match. Instead, they record what happens at each distance.
Before making predictions, the group separates two questions: How much light does a source give off, and how bright does it appear from the observer's position? Their cards must also explain which parts of the lamp investigation can help them reason about stars and which parts do not represent real space.