Using a Planisphere (Middle School and up)

Objective

To learn how to use a planisphere -- the projection on a plane of the celestial sphere; learn to locate constellations, stars, and planets at any time of year. Students should have practice reading a star map before this exercise.

Materials

• Planispheres
• Planisphere kits with instructions for audience to take with them.

Planetarium Set-Up

• Tonight's Sky
• Cardinal Points on
• Lights dim but bright enough to read

Introduction

The rotation of the Earth on its axis causes the stars to rise and set each evening. In addition, the orbit of the Earth around the Sun places different regions of the sky in our night-time view. A chart of the night sky will map the locations of the stars; a planisphere will let us know which stars will be visible during any time of night for any time of year. This exercise will help you become acquainted with our night sky.

Procedure

Instruct the audience on the basic use of a planisphere: "Position the planisphere so that the side with the opening is facing you. Notice on the planisphere that the names of the constellations are given in all capital letters and that the names of the stars are given in smaller letters. Note, too, that the brighter the star is, the larger the circle."

"We are going to step through some exercises that will familiarize you with how to use this planisphere. Some of these steps will be relatively easy; others may be a bit hard. Please feel free to consult with your neighbors and ask me as many questions as you wish!"

A number of people will have quite a bit of trouble with some of the following exercises. Take your time. Walk around helping people; make sure most of the audience has mastered a step in this exercise before moving on. You might wish to pause, at any step, to demonstrate using the planetarium itself.

Exercises

1. The horizon on the Earth is defined as what?

2. The "oval" hole represents the sky. What part of this oval represents the Earth's horizon?

3. Note the outside of the star wheel with the months and days indicated. Set the wheel to the month, day, and time of your birth. That is, line up the time of day with the day and month. If you don't know the exact time, then set the wheel for midnight.

4. Point to the zenith (the place "straight up" on the planisphere and name a star or constellation that was on or close to the zenith when you were born.

5. As you look at the planisphere, does it seem as if West and East are reversed? The planisphere represents a map of the sky. Hold the planisphere as you would if you were really outdoors observing.
   • Pretend you are facing North. How would you hold the planisphere?
   • Turn until you are facing West. What adjustment must you make with the planisphere so that you can accurately read the map? How about when you turn to face South or East?

6. Find the North, East, South, and West horizons.
   • What star was just rising in the eastern sky at the time you were born?
   • What star was setting on the western horizon at the time you were born?
   • What constellation was on the northern horizon? The southern horizon? The northeastern horizon? The southwestern horizon?

7. Why is the North Star in the very center of the planisphere?

8. If you were at the North Pole, where would you find this star?

9. If you were at the equator, where would you find this star?

10. What constellation is this star part of?

11. Turn the planisphere counter-clockwise 360 degrees to represent the passing of 24 hours. Note the date passes through all of the times on the star wheel.
    • What star doesn't seem to move at all?
    • Name three constellations that never set from our location on Earth.

12. Find the dashed-lin circle representing the ecliptic.
    • Name four constellations the ecliptic passes through.
    • The ecliptic represents the path of the Sun against the background stars during the year. Turn the wheel so that it is noon on the day you were born. What signs of the zodiac to you see?

13. Name your favorite constellation.

14. What constellation do you hope to find first in the sky?

15. On the next clear night, go outside with your planisphere and find your favorite (or any other) constellation!