Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

Planetarium model


A home-made planetarium.

Apparatus and materials

Round-bottomed flask, 2 litre

Lamp, 12 V 36 W

Aquadag (colloidal graphite in water)

Clamp stands, 2

Suitable support for flask (see diagram)

Health & Safety and Technical notes

Care is needed to make sure the flask is not dropped. The flask surface will get very hot after a while.

planetarium model using round-bottomed flask

Improvise a planetarium using a two litre round-bottomed flask (preferably the type with a wide neck).
Support a 12 V, 36 W lamp at the centre of the flask. Coat the surface of the flask with Aquadag (colloidal graphite in water). Scratch holes in this surface to represent the pattern of some of the major constellations.



Switch the lamp on in a darkened room. Rotate the flask and the spots of light on the ceiling will rotate and display the simple daily motion.


Teaching notes

1 It is recommended that a model of the Solar System (orrery) should not be shown at this stage unless the heliocentric world of the solar system (the work of Copernicus) has been discussed.
2 Where a visit to a planetarium can be arranged this can be a valuable part of the teaching, particularly if a special programme is arranged. There are many simple planetarium models which can be purchased from Science Museums and toy shops.
This experiment was safety-checked in April 2007