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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 ...
The average annual solar radiation arriving at the top of the Earth's atmosphere is about 1361 W/m 2. This represents the power per unit area of solar irradiance across the spherical surface surrounding the Sun with a radius equal to the distance to the Earth (1 AU).
The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m 2 (watts per square meter) at a distance of one astronomical unit (AU) from the Sun (that is, at or near Earth's orbit). [99]
Because the surface area of a sphere is four times the cross-sectional area of a sphere (i.e. the area of a circle), the globally and yearly averaged TOA flux is one quarter of the solar constant and so is approximately 340 watts per square meter (W/m 2).
Approximating Earth as a sphere, the cross-sectional area exposed to the Sun is equal to one quarter the area of the planet's surface (). The globally and annually averaged amount of solar irradiance per square meter of Earth's atmospheric surface ( I 0 {\textstyle I_{0}} ) is therefore equal to one quarter of TSI, and has a nearly constant ...
Solar flares and coronal mass ejections tend to occur near sunspots, dark patches as big as Earth that are located near the most intense portions of the sun’s shifting magnetic field.
The integral of solar irradiance over a time period is called "solar exposure" or "insolation". [4] [5] Average solar irradiance at the top of the Earth's atmosphere is roughly 1361 W/m 2, but at surface irradiance is approximately 1000 W/m 2 on a clear day.
On December 24, Parker Solar Probe will come within 3.86 million miles (6.2 million kilometers) of the solar surface, closer than any human-made object to the sun.