The amount of solar radiation at all wavelengths reaching the Earth at its mean distance from the Sun; also known as the solar constant. Its average value is 1368 W/m2. The total solar irradiance varies by about 0.1% between solar maximum and minimum, and larger variations are found on a daily basis. The highest values of the TSI are found at solar maximum, because the brightening effect of increased numbers of faculae on the photosphere more than compensates for the darkening effect of sunspots.
Subjects: Astronomy and Astrophysics.