Lab: Measuring Parallax
Background: One of the difficulties in Astronomy is measuring distance.  One of the four ways to measure distance is parallax.  Parallax is the apparent shift in the position of an object when viewed from two locations.  The nearer an object is to the observer, the greater its parallax.   This activity will show how distance affects the amount of observed parallax.

Hypothesis:  Predict what wll happen to the parallax shift  for each of the measurements.

 Materials
meter stick                         masking tape                             metric ruler
 
Procedures:
    1. tape the meter stick onto the table in three different locations: 20 cm, 40 cm, 60  cm. making sure that the 0 cm end is slightly off the table
    2. attach a metric ruler to the end of the meter stick  closest to the  100 centimeter mark to form a T-Shape.
    3. hold a pencil upright at one of the marked positions,starting with the 20 centimeter mark.
    4. close one eye and observe the pencil's position against the metric ruler.  RECORD the the number that is covered by the pencil.
    5. close the other eye and observe the pencil's position against the metric ruler.  RECORD the the number that is covered by the pencil.
    6. determine the observed parallax by finding the difference between these two numbers and Record.
    7. move the pencil to 40 centimeters and repeat steps 4 and 5
    8. then move to 60 centimeters and repeat steps 4 and 5
    9. complete the table with information needed to determine observed parallax.

 Data Table:  __________________________________________________
 

                Which eye
                 20 centimeters
                  40 centimeters
                  60 centimeters 
 
             RIGHT EYE 
.represents first 6-month of viewing		  
 
 .		 . .
             LEFT EYE 
represents second 6-month of viewing		  
 . 
 		 . .
          PARALLAX 
find the difference between the number you see with your right eye and the number you see with your left eye 
        | absolute value | 
 
 		 |Right eye -  Left eye| 
 
 		  |Right eye -  Left eye| 
 
 		   |Right eye -  Left eye| 
 
 
 
Conclusion:  (when you save - leave enough room to write or type in your answer)
 
    1.   What happened to the pencil when the right eye was closed and the left eye was opened?

    2.   What changes in parallax did you calculate as you placed the pencil further away from your eye (comparing parallax at 20 centimeters, 40 centimeters and 60 centimeters)?

    3. If you were to move the pencil further away from zero, where you viewed the pencil, to the 100 centimeter mark, what would you predict the parallax shift to be?

    4.  How does the distance of an object from an observer affect parallax? (this is a general statement about parallax)