solar constant

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The average density of solar radiation measured outside Earth's atmosphere and at Earth's mean distance from the sun, equal to 0.140 watt per square centimeter.

Wiktionary

1. n. The amount of incoming solar radiation per unit area, measured on the outer surface of Earth's atmosphere, in a plane perpendicular to the rays.

GNU Webster's 1913

1. n. (Astron.) the quantity of heat received by the earth from the sun in a unit of time. It is, on the C. G. S. system, 0.0417 small calories per square centimeter per second.

WordNet 3.0

1. n. the rate at which radiant solar energy is received at the outer layer of the earth's atmosphere