Using a flashlight to determine the distance to a star

Name(s): _____________________________     Date: ______________________

We are going to make the observations necessary to calculate the distances to two different stars using the inverse square law.

Work in groups of three.
Each person will make the measurement for each star once and all three people in the group will do their calculations based on the average of the three measurements.
If/Since we have not talked about this in class yet, the analysis will be due after we have measured the brightness of the sun in class.

You will need:

a meter stick and/or a 2-meter stick
a flashlight with one end of a piece of optical fiber taped to the face of the flashlight and the other end taped facing the back of the flashlight aluminum foil to cover the flashlight

The only light that you should see when it is dark out and the flashlight is on is light from the end of the optical fiber. This is your "artificial star" and its brightness is about one millionth (0.000 001 = 1E-6 ) of a Watt.

Follow these steps:

Choose a bright star that you will observe.
```
     Name of bright star:                                           
```
One partner will be the observer, one will hold the "artificial star," and one will measure the distance between the "artificial star" and the "observer's" eye, when the artificial star and the star chosen above appear the same brightness. After the first measurement is recorded, change roles: choose a new observer, measurer, and artificial star holder and repeat. Continue until everyone in your group has been the observer.

Record your measurements of the distance below:

    1st measurement:                                     meters


    2nd measurement:                                     meters


    3rd measurement:                                     meters


    average measurement:                                 meters

Record the value we found for the luminosity of the sun (or look up the value given in the book):
```
     Lsun =                                              Watts
```
Using the same method that we used to find the brightness of the sun in class (the inverse square law of brightness as a function of distance), calculate the distance to the star. Show your work below.

Now, repeat for a second star.

Choose a bright star that you will observe.

     Name of bright star:

Record your measurements for the second star below:

    1st measurement:                                     meters


    2nd measurement:                                     meters


    3rd measurement:                                     meters


    average measurement:                                 meters

Record the value we found for the luminosity of the sun (or look up the value given in the book):
```
     Lsun =                                              Watts
```
Using the same method that we used to find the brightness of the sun in class (the inverse square law of brightness as a function of distance), calculate the distance to the second star. Show your work below.

Now that you've calculated distances to these two stars, based on your own observations, compare your values to those derived by other astronomers.

Look up the distances to the two stars using any method you choose: your textbook, the Voyager software, the web, ...


	Distance to 1st star:                               


	Distance to 2nd star:

Where did you find these values given? Be specific: page number in text, url of web site, etc.
Which star is actually farther away? Does this agree with your answers to parts 4 and 8?
For your first star: is the distance you calculated
```
	larger than 	smaller than 	the same as 	(Circle one.)
```
the distance in the literature?
Was our assumption that the star is equal in luminosity to the Sun correct?
```
    yes     no                                      (Circle one.)
```
How do you know?

If our assumption was incorrect, is the luminosity of the star actually


      larger   or   smaller   than that of the Sun?   (Circle one.)

Explain below.

Use the average distances you found in parts 2 and 6 to find the [apparent] brightness ratio for your two stars.
Which star appears brighter to you?

Look up the apparent magnitudes of the two stars using any method you choose: your textbook, the Voyager software, the web, ...


	Apparent magnitude of 1st star:                               


	Apparent magnitude of 2nd star:

Based on these magnitudes, which star ought to appear brighter? Does this agree with your own observations? Discuss.
Using the apparent magnitudes you looked up and the formula from the book or the method described in class, find the brightness ratio for these two stars.
Do your answers to 15 and 19 agree? Discuss.