The mean intensity of the solar beam in free space (i.e. before penetrating the Earth
's atmosphere) at the average distance of the Earth
from the Sun
. The intensity is not strictly constant for all the wavelengths of radiation involved. The amount of variability is still a subject of debate, but is certainly very small apart from the long-term development in the history of the Sun
solar constant, the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere. The actual value of the energy varies with several factors; the most important factor is the earth's distance from the sun, which changes because of the earth's elliptical orbit. For computing the value of the solar constant, the astronomical unit, or average earth-sun distance, is used.
Steady rate at which energy from the Sun
is received from just outside the Earth
's atmosphere. Its value is c.
1.353 kilowatts per square metre (perpendicular to the Sun's rays).