A simple celestial sphere
To show the apparent movement of the stars through the sky.
Apparatus and materials
Umbrella, plain black
Health & Safety and Technical notes
Make sure the umbrella is in good condition, with no exposed ribs at its edges.
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.
Spin the umbrella to show the apparent movement of the stars.
It is better to avoid the spinning Earth interpretation for beginners.
This experiment was safety-checked in April 2007