Exoplanet Detection

This demo was developed by graduate student Li-Wei Hung

This activity has several parts to it:

Transit Method: This activity involves a large light bulb in the center of a lazy suzan. Wires attached to painted styrofoam balls are used to simulate planets in transit around the central "star." We then set up a light meter to a voltmeter to measure the detected light and move the planets around the star. The voltmeter's large display shows that the detected light dips periodically as the planet orbits. We use different sized "planets" to show how the transit method can be used to determine the size of a planet.

Direct Detection: A large black project board is used to represent space. A small LED light is placed in the center of the board to represent a star. A small dot of reflective paint is placed close to the LED to represent a planet reflecting starlight. A digital camera is set up on a tripod some distance from the board, and students can practice changing the contrast on the camera until they can see the "planet" in the digital camera's screen. The presenter discusses the difficulty of direct detection, and explains why it helps to look at dimmer stars.

Radial Velocity: This part of the demo requires two steps. First, students are introduced to the concept of the Doppler Effect using a tuning fork (or, alternatively, a electronic instrument tuner). After demonstrating that the tuning fork plays a single frequency when struck, swing the tuning fork in a circle above your head to produce an oscillating frequency. Explain that this effect is seen with light waves as well as sound waves. Then you can introduce the concept of a radial velocity "wobble." We use two styrofoam balls attached by a small wooden dowel. We explain that planets and stars that are orbiting their common center of mass are bound to each other gravitationally (this is modelled by the wooden dowel). When you try to spin the larger styrofoam ball in place, it will wobble due to the effect of the adjoined "planet" or star". Thus you can demonstrate the effect that a bound body has on the larger body's orbit. You can show that the effect is larger when the orbiting body is larger in size.