A balloon-borne infrared coronagraph.

A stratospheric balloon-borne coronagraph operating at wavelength 2.2 micro has been successfully flown in order to observe the outer solar corona. The system employed external occultation with three straight edges, and the Lyot portion was axial. Scanning of the corona was accomplished through rotation of the rear Lyot section about a diameter of the primary objective lens. A description of the origins of stray light in the instrument is given, and measurements at wavelengths 0.5 micro, 0.8 micro, and 2.2 micro presented. A wavelength dependence of the scattered light from the objective lens is deduced. Some details of the detection system and solar tracking are discussed.