# Labs from YSI 95 : Calculating The Moon's Width.

April Whitt
CARA Yerkes Summer Institute, August 1995

Adapted by Joan Hall for Project SPICA from Ovid K. Wong's "How Wide is the Moon?" The Science Teacher, October 1987.

This is the staff copy of the lab.

## Objective:

Students will indirectly measure the width of the Moon.

## Materials needed:

• 3x5 index cards
• meter sticks
• pencils
• scissors

## Procedure

1. On one long edge of an index card, mark the center. Cut a 2.5 square cm slot centered on that mark.

2. On the opposite long edge, mark the center. Draw a 5 cm long line centered on that mark, parallel to the long side and at least 1 cm from the edge. Cut through the card on that line so that there's a slit .

3. Push the card onto a meter stick (meter stick goes through the slit). You should be able to slide the card back and forth along the stick.

4. At night, when the Moon is full (or close enough to see the whole diameter), slide the card down to the 100 cm end. Hold the zero end of the meter stick just touching your cheek, with the 100 cm end (and the card) pointing at the Moon.

5. Slide the card along the meter stick until the Moon just fills the slot in the card. (It helps to close one eye while sighting along the stick.) Record the distance between your eye and the card.

6. Calculate the width of the Moon using equal proportions. The relationship can be expressed as

```		width of slot				width of Moon
________________________	=	_________________________
distance from card to eye		distance from card to Moon
```
The distance from Earth to Moon is about 384,400 km.

Adapted by Joan Hall for Project SPICA from Ovid K. Wong's "How Wide is the Moon?" The Science Teacher, October 1987.

Important Disclaimers and Caveats: