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Solar luminosity
 
 
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The solar luminosity, , is a unit of luminosity
Luminosity

Luminosity has different meanings in several different fields of science....
 (power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
 emitted in the form of photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
s) conventionally used by astronomer
Astronomer

An astronomer is a scientist who studies Celestial body such as planets, stars, and Galaxy.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws....
s to give the luminosities of star
Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
s.






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The solar luminosity, , is a unit of luminosity
Luminosity

Luminosity has different meanings in several different fields of science....
 (power
Power (physics)

In physics, power is the rate at which mechanical work is performed or energy is transmitted, or the amount of energy required or expended for a given unit of time....
 emitted in the form of photon
Photon

In physics, the photon is an elementary particle, the quantum of the electromagnetic field and the basic unit of light and all other forms of electromagnetic radiation....
s) conventionally used by astronomer
Astronomer

An astronomer is a scientist who studies Celestial body such as planets, stars, and Galaxy.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using physical laws....
s to give the luminosities of star
Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
s. It is equal to the current accepted luminosity of the Sun
Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
, which is 3.839 × 1026 W
WATT

WATT is a radio station broadcasting a News radio-Talk radio-Sports radio format. Licensed to Cadillac, Michigan, it first began broadcasting in 1945....
, or 3.839 × 1033erg
Erg

An erg is the unit of energy and mechanical work in the Centimetre gram second system of units system of Units of measurements, symbol "erg"....
/s. Note that the Sun is a weakly variable star
Variable star

A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth....
 and its luminosity therefore fluctuates.

Calculating with this constant


You can calculate how much solar power hits the Earth by comparing a cross sectional area of the Earth and the total surface area of a sphere with a radius equal to the distance of the earth from the sun.
  • The Earth's radius is 3,963 miles (6,378 km.).
  • The Earth's cross sectional area = p×radius2 = 49.3 million square miles (128.000.000 kmē).
  • The Sun's average distance is about 93,000,000 miles (150.000.000 km.).
  • The surface area of a sphere
    Sphere

    A sphere is a symmetrical geometrical object. In non-mathematical usage, the term is used to refer either to a round ball or to its two-dimensional surface....
     = 4×p×radius2 = 1.09×1017 square miles (2.82×1017 kmē).
  • Power reaching the Earth = P(total) × Area(earth)/Area(sphere) = 1.77×1017 W.
  • The power hitting a square meter of area on Earth: (square meter = 1/16092 square miles)
    • Power over square meter = P(total)(1/16092)/area(sphere) = 1387 W (the solar constant)
  • Estimates have been made that humans use about 12×1012 W.
  • How much land area would be needed to power that?
    • The best solar cells can produce about 33% efficiency.
    • Area needed = 12×1012/(1387×0.33) = 26×109 m2 = 10122 square miles ~100×100 mile square. (More is needed since the sun is not always straight over head, and because some fraction of the radiation does not reach the surface due to clouds and atmospheric scattering.)