**Observing the Planetarium Sky Worksheet**

Time (minutes) | Number of Stars |
---|---|

0 minutes | |

- What does your graph tell you about the number of stars you can see at different times? What is physically happening to you to cause this change?
- Calculate the rate at which stars become visible? (Remember the
*rate*is the slope of the graph: the change in "y" divided by the change in "x". Show all calculations.) - What are sources of error in this rate?
- If we observed for another 5 minutes, what would the graph look like? In
a different color sketch your prediction for the second 5 minutes on the graph.
Explain your prediction.
- The area of your pupil is proportional to its radius squared
[area = *(radius)
^{2}]. Suppose that during the 5 minutes of your observations, the size of your pupil grows from 2 mm to 6 mm in diameter. What is the ratio of the area of your dark-adapted pupil to the bright-adapted pupil? (Show all calculations.) - The amount of light that enters your eyes is proportional to the area of
your pupil. Did the light-gathering power of your eye increase or decrease
over time? By what factor?
- An average-sized amateur telescope is about 20 cm (200 mm) in diameter;
the largest ground-based astronomical telescope is currently about 10 m
(10,000 mm) in diameter. Compare the light-gathering power of an amateur
telescope to the best light-gathering power of your eye. Compare the
professional telescope to the best light-gathering power of your eye. Show
all calculations.
- Why were ancient astronomers so limited in their observations of the sky?
- Given today's technology, how would we observe fainter objects?