LightGrapher Flash Applet

...turns your webcam or built-in computer camera into a makeshift light sensor to display graphically the brightness of a model star (a lightbulb or even light-colored ball). When a [darker-colored] planet passes in front of the star, the brightness drops and a dip in the graph occurs. The software receives real-time data from the external webcam or internal computer camera. It was made for use with the orreries described on this page (above). It may be run either directly from this page or downloaded and run locally in your browser.

Download LightGrapher

This is a Flash file that can be downloaded and run in a few ways:

See also update specifically for FOSS teachers.


DIRECTIONS for using LightGrapher:

    1. Set up planet(s) to orbit the model star (light bulb or white sphere).

    2. Start the software and click on "Allow" to let brightness data to come in from the camera.

    3. Aim the camera at the model star and center the targeting circle on the model star in the camera view.

    4. Alter the height of the camera/laptop or the star-planet model so that the planet(s) actually pass in front of the star as seen by the camera view. [The camera must be in the planets' orbit plane.]

    5. Set the size of target circle to fit the star using slider on right of screen. Making the targeting circle slightly smaller than the star is better than having it slightly larger than the star.

    6. If desired, change duration of "Capture Data" (default time = 30 seconds)

    7. Click "Capture Data" button and make planet(s) orbit.

    8. To adjust vertical scale, either click "Autoscale" or manually enter minimum and maximum % values at bottom and top of y-axis.

    9. You may click Pause button, then Resume, anytime during Data Capture.

    10. You can "Save" the data for any trial as a .png graphics file that you can open in a graphics program.

TIPS for using LightGrapher:

    • It's best not to move the camera during a trial.

    • This software works best with

    • - a light bulb as the model star at a distance of 1 meter or less, or

    • - an opaque light-colored (or white) sphere as the star at a distance of 60 cm or less. In truth, the closer the model is to the camera, the better, but be sure to point out to students that the model represents a situation where the camera/spacecraft is light-years away from the star.

    • In general, slower cranking and larger target sizes gives better results.

    • In darker environments, the webcam requires more exposure time for each frame effectively decreasing the frame rate, so crank the orrery more slowly if surroundings are dark.

    • If the environment is dark, using a light bulb as model star is preferable to a white sphere.

    • If Autoscale is used, it may be necessary to reset Min and Max values on the vertical scale manually before a new trial, if lighting conditions change.


LightGrapher used in the Telescopes to Tanzania campaign.

Chuck Ruehle demonstrates to Tanzanian students how to use the LightGrapher program to learn about planet transits and the search for ExoPlanets. The interactive program, from NASA's Kepler Space Telescope site, provides a hands on teaching tool for students. Photo by Susan Ruehle. This software is © 2011 (version 1) and © 2012 (versions 2.0 and 3.0) by the Regents of the University of California. As a product of the NASA Kepler mission Education team, it may be used freely without charge.