Solar constant

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The Solar constant (denoted as S☉ by the IAU standard) is a mathematical equation averaging the amount of energy received by a given area one astronomical unit away from the Sun. To put it simply, it is measuring the amount of energy per second per square meter that arrives from the Sun at the distance of Earth's orbit. More specifically, it is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit area. It is measured on a surface perpendicular to the rays, one astronomical unit (au) from the Sun (roughly the distance from the Sun to the Earth). The solar constant includes radiation over the entire electromagnetic spectrum. It is measured by satellite as being 1.361 kilowatts per square meter (kW/m2) at solar minimum (the time in the 11-year solar cycle when the number of sunspots is minimal) and approximately 0.1% greater (roughly 1.362 kW/m2) at solar maximum. The solar "constant" is not a physical constant in the modern CODATA scientific sense...

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