Geometric albedo compares a body's full-phase brightness with that of a flat, perfectly diffusing reference disc of the same cross-section.
Geometric albedo is a measure of the reflectivity of a celestial body, such as a planet, moon, or asteroid, as observed from a specific geometrical configuration. Specifically, it defines the ratio of the brightness of the object when illuminated by a light source (usually the Sun) to the brightness of a flat, fully reflective surface (like a perfect diffuser) under the same illumination conditions.
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