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 (oriented normal to the Sun's direction) at the distance of one astronomical unit (the average distance from the Earth to the Sun). It is currently equal to about 1361 watts per square meter in vacuum (outside the Earth's atmosphere). 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 will increase significantly.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".