Abstract: A split-sphere observatory enclosure includes an antrum and a rotor including an oculus. The oculus is covered by an oculus window, which is rotatably mounted to the rotor. As an instrument housed by the enclosure moves to track an object or point across the sky, the oculus window is rotated to maintain a fixed orientation with respect to the instrument.

Abstract: A split-sphere observatory enclosure wherein the antrum segment is capped with a shutter lid. The rotor which is the active shutter segment sweeps through an elongate curved aperture in the shutter lid to reveal the oculus. The oculus may be completely covered by the shutter lid or completely exposed at any elevation between the horizontal and vertical or zenith positions. The weather resistance of the enclosure is enhanced through the provision of continuous seals between the segments.