What is the best way to track the sun for a two axis solar tracker?

[monahago]

ineed your help please ihave two stepper motors and iwant to used in two axis solar tracker but ihaving aproblem in the light sensor icant decided yet the pest kind of sensor,and there are need to use aposition sensor also in my plant.

 

[Topher925]

I've built a two axis solar tracker before using 3 photo-resistors. By comparing the voltage across any two of the resistors angled slightly away from each other you can determine an intensity gradient from the light source to track.

The ultimate solution would be to use a CCD camera aimed at the sun.