It is a solar tracker based on an atmega8 and two light depending resistors.
The two voltages across the LDRs are compared and the ideal position in relation to the sun is detected.
For the "night mode" the atmega detects threw the LDRs that it is dark and turns the motor to the east position and waits for the sun.
It was a cloudy day, so there was no direct sunlight, only diffuse light. Because of that, the tracker does not always go back to the same angle .