Detecting exoplanets

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.