Midnight Sphere

A Midnight Sphere was a spherical shell of gas and plasma capable of absorbing light and sensor beams, first theorized by Dr. Culla sometime prior to 2268.

In 2268, Commodore Bishop planned to create a Midnight Sphere to enclose "The Yard", a secret Starfleet facility, and recruited Spock to help do so. The resulting field encompassed a volume three-quarters that of Earth, though it also emitted hazardous plasma waves beyond the sphere surface, making its use impractical. (SS TOS (Devices and Desires))