Name______Date Submitted______

Brightness vs. Distance of Stars

Purpose

In this inquiry, we are going to look at the relationship between brightness and distance, and to compare this relationship to stars in the universe.

Procedures

  1. We will be doing this as a class. 40 W, 60 W and 100 Watt light bulbs will be setup in the back of the classroom. I will turn on/off all light bulbs. As I do, answer the following question:
  2. Can you tell the differences in the brightness between the bulbs?

______

  1. Move 5 m toward the 40 W bulb.
  2. Does the light look brighter than the 60 W bulb? ______

Explain your answer: ______

  1. Does it look brighter than the 100 W bulb? ______
  1. Shift the positions of the bulbs so that the 40 W and the 100 W bulbs are in the back of the room and the 60 W is halfway between you and the other lamps.
  2. How do the brightness levels compare? ______
  3. Using the light meter, test one bulb at a time.
  4. Design a data table to record your light meter readings for each of the bulbs.
  5. Record the brightness of each of the bulbs at different distances. Note: You are to determine the distances, but make sure your distances increase at a constant rate.
  6. Graph the brightness vs. the distance from source for each bulb on 1 sheet of graph paper.
  7. Plot the distance on the horizontal (X) axis and brightness on the vertical (Y) axis. Leave room on the graph so that you can extrapolate the graph beyond the data you have collected. Plot the data for each bulb and connect the points.
  8. Extrapolate the data by extending the lines on the graph using dashes.
  9. Use your graph to answer the following questions:
  10. Explain the general relationship between wattage and brightness (as measured by your light meter). ______
  11. What is the general relationship between distance and brightness? ______
  12. Do all of the bulbs follow the same pattern? Explain your answer. ______
  13. Draw a light, horizontal line across your graph so that is crosses several of the lines you have graphed. Does a low wattage bulb ever have the same brightness as a high wattage bulb? ______Describe one or two such cases in your data ______
  14. The easiest way to determine the absolute brightness of objects of different brightness and distance is to move all objects to the same distance. How do you think astronomers handle this problem when trying to determine the brightness and distances to stars? ______
  15. Think about the relationship between brightness and distance to the stars you see at night in your community. Does this relationship hold true for all stars that you observe in the night sky? Explain why or why not. ______
  16. Are there any other techniques that astronomers use to determine brightness and distances to stars? ______List and describe 2 other techniques, if they exist. ______