4.Main Content
experiments
A simple celestial sphere
Demonstration
To show the apparent movement of the stars through the sky.
Apparatus and materials
- Umbrella, plain black
Technical notes
1 A simple model can be made from an ordinary umbrella. The star pattern drawn will depend upon your terrestrial location. You may be able to find a suitable star chart from the internet. For those in the northern hemisphere, when it is opened, the ferrule can represent the Pole Star, and constellations such as the Plough and Cassiopeia can be represented by paper discs stuck in the appropriate places to the underside of the umbrella, as shown in the diagram.
Chalk marks are not satisfactory: they tend to rub off when the umbrella is closed again. The eight ribs provide a useful guide in the marking up. Pairs of ribs enclose 45° (or three hours of time). The surface can include the circumpolar stars visible from your latitude.
2 An alternative would be to use a model of the celestial sphere.
Safety
Make sure the umbrella is in good condition, with no exposed ribs at its edges.
Read our standard health & safety guidance
Procedure
Spin the umbrella to show the apparent movement of the stars.
Teaching notes
It is better to avoid the spinning Earth interpretation for beginners.
This experiment was safety-checked in April 2007