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Table of Contents

How Many Stars?

Data card: side one

This activity should be done on a clear moonless night. It is best to have no clouds, although a few scattered clouds are permissible provided that only clear unobscured sky is used for the star count.


The procedure is simple:

1. Obtain (or make) a hollow cylinder about 25 -35 cm in length, and with a diameter of 4 to 6 cm.

2. Hold the end of the tube up to your eye and count the number of stars that you can see through the tube without moving the tube. NO CHEATING! If you see no stars through the tube you must count zero. Don't move the tube around to look for stars.

3. Record this number (on your printed copy of the chart provided).

10 random samples

HINT: Allow your eyes to become "dark-adapted", by allowing yourself at least 20 minutes outside, away from bright light, before you begin this activity.

4. Repeat the counting procedure ten times, each time selecting a different direction in the sky.

Choose the directions at random. Do not move the tube to see more stars or to select brighter stars.

5. Record the number of visible stars that you can see for each observation.

Print out the accompanying chart on which to record your results and peform your calulations.

This chart will also provide you with a series of step by step calculations which you can perform in order to determine the total number of stars visible to the naked eye at your observing location.

The graph included on this chart is a guide to determining the quality of the sky conditions in your neigbourhood.

If the total number of visible stars is large, you have excellent sky conditions. If the total number of visible stars is small, then you have a problem. It may be haze, smog, light pollution, or a combination of these conditions.


Préparé par l’équipe scientifique YES I Can! à l'Université McMaster,
pour l'Agence spatiale canadienne