polestar recorder

polestar recorder

[′pōl‚stär ri‚kȯrd·ər]
(engineering)
An instrument used to determine approximately the amount of cloudiness during the dark hours; consists of a fixed long-focus camera positioned so that Polaris is permanently within its field of view; the apparent motion of the star appears as a circular arc on the photograph and is interrupted as clouds come between the star and the camera.