This simulator shows what happens when an extrasolar planet passes in front of its star. Such eclipses (called transits) allow scientists to detect planets they would not see otherwise.
The upper left panel shows the star and planet as they would be seen from earth if we had an extremely powerful telescope. In fact, this privileged view is impossible with any existing telescope; astronomers must infer the transit from the dip in the lightcurve as the planet moves in front of the star. (A lightcurve is a plot of brightness over time.)
The lightcurve is shown in the upper right panel. The apparent brightness of the star is 'normalized', that is, the brightness is reported as a fraction of the full brightness (when the star is not eclipsed). You have the option of showing simulated noisy measurements and hiding the theoretical curve — this gives a better idea of what it is like working with real data.
The planet, star, and system properties can be set in the lower panels. These parameters can also be set by selecting one of the presets from the dropdown menu in the Presets panel.