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The solar constant is an average of a varying value. In the past 400 years it has varied less than 0.2 percent. [2] Billions of years ago, it was significantly lower. This constant is used in the calculation of radiation pressure, which aids in the calculation of a force on a solar sail.
The constants listed here are known values of physical constants expressed in SI units; that is, physical quantities that are generally believed to be universal in nature and thus are independent of the unit system in which they are measured. Many of these are redundant, in the sense that they obey a known relationship with other physical ...
Dimension Comments Amount of substance: n: The quantity proportional to the number of particles in a sample, with the Avogadro constant as the proportionality constant: mole (mol) N: extensive, scalar Length: l: The one-dimensional extent of an object metre (m) L: extensive: Time: t: The duration of an event: second (s) T: scalar, intensive ...
Solar radiation pressure on objects near the Earth may be calculated using the Sun's irradiance at 1 AU, known as the solar constant, or G SC, whose value is set at 1361 W/m 2 as of 2011. [17] All stars have a spectral energy distribution that depends on their surface temperature. The distribution is approximately that of black-body radiation.
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]
The flux density of the incoming solar radiation is specified by the solar constant S 0. For application to planet Earth, appropriate values are S 0 =1366 W m −2 and α P =0.30. Accounting for the fact that the surface area of a sphere is 4 times the area of its intercept (its shadow), the average incoming radiation is S 0 /4.
In SI units, the values of c, h, e and k B are exact and the values of ε 0 and G in SI units respectively have relative uncertainties of 1.6 × 10 −10 [16] and 2.2 × 10 −5. [17] Hence, the uncertainties in the SI values of the Planck units derive almost entirely from uncertainty in the SI value of G.
Any ratio between physical constants of the same dimensions results in a dimensionless physical constant, for example, the proton-to-electron mass ratio. The fine-structure constant α is the best known dimensionless fundamental physical constant. It is the value of the elementary charge squared expressed in Planck units. This value has become ...