Orbital motion of planets
Earth and Space

The transit method

Practical Activity for 11-14 IOP RESOURCES

In this activity students use a lamp and polystyrene balls to model how astronomers detect exoplanets using the transit method.


Apparatus and materials

  • Lamp (one with an opal globe light bulb is ideal)
  • Polystyrene balls of assorted sizes
  • Bamboo barbecue skewers (with a length of approximately 30 cm)
  • Webcam
  • Light Grapher software

Each student will require a photocopy of the instructions and worksheet.

Health & safety and technical notes

Ask students to be careful when building models as skewers may be sharp. Warn students not to stare directly into the lamp. This activity uses a piece of software called Light Grapher which detects input from a webcam to graphically display the brightness of a model star.

The practical activity

  1. Students should set up a lamp to represent their star and attach a ball to a stick or skewer to represent their exoplanet.
  2. They should then move their ball on skewer/stick across the front of their lamp and produce a light-curve. You will need to explain how to use the Light Grapher software.
  3. Once students have produced a single light-curve, they should predict how the shape of the light curve will change for a bigger and faster exoplanet. Encourage them to think about which variables they need to keep constant (e.g. radius of orbit) in order to test their predictions.

Download the resources

The resources below include teacher notes, a student worksheet and instructions. 

IOP DOMAINS Physics CPD programme

Energy CPD videos

Our new set of videos gives teachers and coaches of physics a preview of the training we offer ahead of this term's live support sessions.

Find out more