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# Big Dipper

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Author: Janice VanCleave

So You Want to Do a Project about Star Distances!

### Purpose

To determine the daily motion of the Big Dipper.

### Materials

• drawing compass
• 12-inch (30-cm) -square piece of poster board
• ruler
• scissors
• pen
• pushpin

### Procedure

1. Use the compass to draw two circles on the poster board, one with a 6-inch (15-cm) and the other with a 5-inch (12.5-cm) diameter. Cut out the circles.
2. Photocopy the Star pattern shown here. Cut out the pattern and glue it to the small circle (star wheel). (The outer time wheel pattern will be used in the following experiment.)
3. Use the pushpin to make a hole through the center of each circle, then assemble the two pieces by putting the star wheel on top of the larger circle (outer wheel) so that the holes in the center line up. NOTE: The North Star is in the center of the star wheel.
4. Insert the paper brad through the holes to hold the wheels together.
5. Holding the outer wheel, rotate the star wheel in a counterclockwise direction one full turn. Observe the movement of the Big Dipper in relation to the North Star.

### Results

The stars of the Big Dipper move counterclockwise around the North Star (Polaris).

### Why?

The apparent motion of stars results from the rotation (turning) of Earth on its axis (animaginary line that passes through the center of an object and around which the object rotates). The daily circular path of stars is called their diurnal circle.

Since the stars of the Big Dipper appear to move around the North Star each day, they can be used to determine time. A project question might be, How can the movement of the Big Dipper be used to tell time?

1. The wheels can be used to construct a star clock.
2. Prepare a time wheel by dividing half of the outer wheel into 12 equal parts. Labelthe parts from 6 P.M. to 6 A.M. as shown.
3. After dark on a clear night, face north and locate the Big Dipper above the northern horizon.
4. Turn the star wheel until the outline of the Big Dipper lines up with the Big Dipper's position in the sky.
5. Turn the time wheel until the time lines up with the date of the observation.
• Repeat the previous steps, making observations about every hour for 3 or more hours. NOTE: Compensate for daylight saving time when it is in effect by adding 1 hour.

### References and Project Books

Baker, Robert H., and Herbert Spencer Zim. Stars: A Guide to the Constellations, Sun, Moon, Planets, and Other Features of the Heavens. New York: Golden Press, 1985.

Chartrand, Mark R National Audubon Society Field Guide to the Night Sky. New York: Knopf, 1995.

Couper, Heather, and Nigel Henbest How the Universe Works. Pleasantville, N.Y.: Reader's Digest, 1994.

Harrington, Philip, and Edward Pascuzzi. Astronomy for All Ages. Guilford, Conn.: Globe Pequot Press, 1994.

Moche, Dinah L. Astronomy: A Self-Teaching Guide. New York: Wiley, 1996.

Moeschl, Richard. Exploring the Sky. Chicago: Chicago Review Press, 1993.

Pasachoff, Jay M. Peterson First Guides: Astronomy. Boston: Houghton Mifflin, 1997.

VanCleave, Janice. Janice Van Cleave's Astronomy for Every Kid. New York: Wiley, 1991.

_____.janice VanCleave's Constellations for Every Kid. New York: Wiley, 1997.

Wood, Robert W. Science for Kids: 39 Easy Astronomy Experiments. Blue Ridge Summit, Pa.: Tab Books, 1991.