This page collects documents, images, source codes and formulas about “heliostats”, “special mirrors” used to make solar light static while sun crosses the sky.
Ancient mechanisms: spring-loaded heliostats (no electricity, no sensors, no chips!)
Stationary heliostats - A pseudo-heliostat can also be built by using a stationary mirror: if the mirror is flat, the reflection will quickly move away from the target, but if the mirror is curved, somthing intriguing happens! Read here the details.