There is some confusion concerning the words "siderostat", "lunastat", "heliostat", "ceoleostat", and "beam director" due to how the various configurations are presently used compared to historical usage.

We define a siderostat as an altitude over azimuth (Alt-AZ) gimbal mounting a single optical flat mirror. We define a heliostat as an equatorially mounted optical flat mirror that directs light along the polar axis either upward or downward. A lunastat may take either configuration. A ceoleostat is typically a siderostat, but again the word is poorly defined. A beam director can take the form of a siderostat, or a Coude' telescope of Alt-AZ, Alt-Alt, or equatorial configuration.