How do I use a photodiode for arduino? I am doing a project that requires me to program an arduino to sense changes of a steady stream of light due to the scattering of that light. If the phootodiode does change its resistance to the current, then a flap will turn a certain number of degrees. I'm not sure how to operate a photodiode, but know the basics of how it works.

The apparatus is designed to increase the operating life of a solar panel on Mars. When dust from a dust storm collects on its surface, a photodiode will detect the change in light and change its resistance to a current running through it. Then a flap connected to the solar panel will close to cover the solar panel. I'm using Hitec HS-311 Standard servo to rotate  the flap, but I've had some problems operating it.
try to use an opamp to create a voltage output from the diode. you can then adc that voltage output from the mcu.