Definition and Illustration of Phase Angle

Word of the Week: Phase Angle

A measurement (from 0 to 180 degrees) of the angle between an observer (such as a spacecraft), the object being observed (such as a planet or asteroid), and a light source (such as the Sun).

OSIRIS-REx will observe asteroid Bennu from low and high phase angles in order to better understand how the asteroid’s surface reflects light.

Credit: University of Arizona

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