Full Option Science System (FOSS) is a Lawrence Hall of Science (LHS) research-based project with more than 25 years experience in developing successful active-learning science curricula for grades K-8. FOSS program materials are designed to meet the challenge of providing meaningful science education for all students in diverse American classrooms. Development of the FOSS program was, and continues to be, guided by advances in the understanding of how youngsters think and learn.

The kit for FOSS Planetary Science course has an excellent orrery for use in Investigation 10, but does not include a light sensor, required for generating real-time graphs (light-curves) with the orrery. Fortunately, LightGrapher is a Flash applet available for free at the Kepler LightGrapher web page.

It turns your webcam or built-in computer camera into a makeshift light sensor to display graphically the brightness of the model star so that when a 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 may be run either directly from the Kepler LightGrapher page or downloaded and run locally in your browser.

LightGrapher Version 3.0, released 2012 Sep 14, is a major upgrade that

• allows for use in rooms with ambient (non-dark) light, as in most classrooms,
• works with either a light bulb as model star or simply a light colored ball,
• has improved targeting control with a wider ranging slider to define target (star) size,
• is not affected by background movements,
• runs reliably every time.

If you prefer to Download LightGrapher it can be opened locally with any Flash-enabled browser. Simply download from the Kepler LightGrapher website and use the "Open" command in your browser to launch it.

DIRECTIONS:

1. Set up the orrery with planets to orbit the model star.
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 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:

• 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 you use Autoscale, you may need to manually reset the Minimum and Maximum values for the vertical scale, for subsequent trials, if lighting conditions change.