Hold your thumb up at arm's length in front of you.  Imagine lines drawn 
from either side of your thumb to a point on  the pupil of your eye.  The 
angle formed by these two lines is a kind of measure of the width 
(diameter) of your thumb, known as the Angular Diameter.  Hold your 
thumb up at arm's length again, and move it closer to your eye.  What 
happens to the angular diameter?  As you can see, the value of an
 objects angular diameter depends upon the distance from the observer 
to the object.  You are going to use this same idea to measure the 
diameter of the moon.

MATERIALS NEEDED:  Meter stick, pencil, index card, thumbtack, 
hole puncher

PROCEDURE

1-Punch a hole in the center of an index card.
2-Thumbtack the index card on the zero end of the meterstick so that 
you can see along  the length of the stick when you look through the 
hole.
3-Point the stick at the moon.
4-Slide the pencil back and forth along the meterstick, until the 
thickness of the pencil just covers the width of the moon. If you have 
short arms, you may need someone else to slide the pencil back and 
forth.
5-Read the distance from the pinhole to the pencil, to the nearest tenth 
of a centimeter.
6-Measure the diameter of the pencil, to the nearest tenth of a 
centimeter.
7- Using your textbook, look up the distance to the moon in kilometers.

Pencil diameter________________cm  Distance from pinhole to
 eye______________cm

Distance to moon  __________________km

Using the data above, set up a proportion and solve for the diameter of
 the moon.  You must show your proportion and how you solved it.