One of the broad streaks that radiate from some craters on the moon, especially Copernicus and Tycho; they consist of material of high reflectivity and are seen from earth best at full moon.

A straight- line segment emanating from a point. Also known as half line.

A curve whose tangent at any point lies in the direction of propagation of a light wave.

A moving particle or photon of ionizing radiation.

Any of about 350 species of the elasmobranch order Batoidea having flattened bodies with large pectoral fins attached to the side of the head, ventral gill slits, and long, spikelike tails.