DISC
, or Disk, the body or face of the sun or moon; such as it appears to us; for though they be really spherical bodies, they are apparently circular planes.
The diameter of the disc is considered as divided into 12 equal parts, called digits; by means of which it is, that the magnitude of an eclipse is measured, or estimated.—In a total eclipse of either of those luminaries, the whole disc is obscured, or darkened; in a partial eclipse, only part of them.
Illuminated Disc of the Earth. See Circle of Illumination.
Disc, in Optics, the magnitude of a telescope glass, or the width of its aperture, whatever its figure be, whether a plane, convex, meniscus, or the like.
