Star projectors are a cheap and visually impressive way to educate your friends and family about the night sky. By placing holes that light can pass through in an opaque sphere that surrounds a light source, you can project accurate reproductions of the night sky onto the surface of any darkened space. This is the same principle by which many planetariums and expensive retail star projectors operate, and it should provide ample illumination for most small to medium-sized rooms.
Go to your local library. Track down a "Goode homolosine"-style star map of the night sky -- it's the type of map projection that resembles an orange peel with ragged edges. Photocopy this map onto paper large enough to wrap around your fishbowl. Then cut out your star map with scissors, carefully following the jagged border.
Place the empty fishbowl upside down over the lamp. If the lamp already has a shade, remove it first.
Wrap the cut-out map around the fishbowl. Once the fishbowl is covered and the ends of the map meet up, secure the map in place with tape.
Carefully poke holes through whatever stars on the map you would like your star projector to display. For each hole you poke, place a dollop of adhesive putty on the glass on the other. Place larger dollops for brighter stars, and smaller dollops for dimmer stars.
Remove the map from the fishbowl, then paint over the surface of the fishbowl with black paint. You may wish to use several coats to cut down on stray light that bleeds through. Then, while the paint is damp but not runny, carefully peel off all the dollops of adhesive putty.
Set up your star projector in a central location in a darkened room. When you turn the lamp on, light will stream through all the glass that was protected from paint by the putty, projecting your "stars" onto the surroundings.
For best performance, try to find a bulb for your lamp that is bright but has as small a filament as possible. Alternatively, consider using a frosted semi-opaque bulb instead of a fully transparent bulb with a large filament. Depending on the size of your fishbowl, you may have to scale down or scale up the size of the star map when copying it. There are a lot of stars in the sky -- consider only displaying stars brighter than a certain magnitude in order to make your star projector more manageable.
Let remaining paint dry thoroughly before use. Always paint in a well-ventilated area.
Things you need
- Large paper
- Spherical fish bowl (ideally with diameter 16 inches or more)
- Black paint
- Adhesive putty