Disk used in telescopes to block a bright object
An occulting disk is a small disk placed centrally in the eyepiece of a telescope or at its focal point, to block the view of a bright object so that fainter objects can be seen more easily.
The coronagraph, at its simplest, is an occulting disk in the focal plane of a telescope, or in front of the entrance aperture, that blocks out the image of the solar disk, so that the corona can be seen. Starshade is one designed to fly in formation with a space telescope to image exoplanets.
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