I instrument demonstrated that the energy output of the sun was variable on the scale of seconds to years. Virtually all life on Earth depends on the sun for energy. Although it appears constant, the total amount of energy radiated by the sun is constantly changing, on scales of seconds, to years, to centuries. Total solar irradiance is the light energy coming to the Earth, most being in the wavelengths from 200 to 2000 nanometers. To calculate the sun's heating of Earth's climate system, the first thing a researcher needs to know is the amount of energy that reaches the Earth from the sun.
Separate instruments measure the amount of light that is reflected from the Earth.
This absorbed energy determines the Earth's average temperature. The differences in the absorption at equatorial versus polar latitudes, and at the surface versus in the clouds, are responsible for driving the fluid motions that control weather and climate. Continuous measurements of solar irradiance go back just over 20 years. Much longer-term monitoring is necessary to fully understand the effect of solar variability on climate. An important consideration in the solar irradiance measurement is that it must be made for a very long time.