Glossary term: Solar Constant

Description: The solar constant is the average amount of electromagnetic radiation (light energy) from the Sun that is received per unit area at the distance of 1 astronomical unit (roughly the average distance from Earth to the Sun). It is currently equal to about 1361 watts per square meter. While not a physical constant, it varies by less than 0.2% over hundreds of years. However, because Earth's orbit is elliptical the flux density at the distance of Earth varies by 7%. As the Sun evolves it is slowly getting brighter, so over billions of years this value changes significantly.

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