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The solar "constant" is not a physical constant in the modern CODATA scientific sense; that is, it is not like the Planck constant or the speed of light which are absolutely constant in physics. The solar constant is an average of a varying value. In the past 400 years it has varied less than 0.2 percent. [2]
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]
For example, when the sun is more than about 60° above the horizon (<30°) the solar intensity is about 1000 W/m 2 (from equation I.1 as shown in the above table), whereas when the sun is only 15° above the horizon (=75°) the solar intensity is still about 600 W/m 2 or 60% of its maximum level; and at only 5° above the horizon still 27% of ...
Solar Cycles Start (Maximum) Spotless days [10] Solar cycle 10–11 1860 – Feb 406 Solar cycle 11–12 1870 – Aug 1028 Solar cycle 12–13 1883 – Dec 736 Solar cycle 13–14 1894 – Jan 934 Solar cycle 14–15 1906 – Feb 1023 Solar cycle 15–16 1917 – Aug 534 Solar cycle 16–17 1928 – Apr 568 Solar cycle 17–18 1937 – Apr 269
The astronomical unit of time is a time interval of one day (D) of 86400 seconds.The astronomical unit of mass is the mass of the Sun (S).The astronomical unit of length is that length (A) for which the Gaussian gravitational constant (k) takes the value 0.017 202 098 95 when the units of measurement are the astronomical units of length, mass and time.
Evolution of the solar luminosity, radius and effective temperature compared to the present-day Sun. After Ribas (2010) [1] The solar luminosity (L ☉) is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun.
In practice, the masses of celestial bodies appear in the dynamics of the Solar System only through the products GM, where G is the constant of gravitation. In the past, GM of the Sun could be determined experimentally with only limited accuracy. Its present accepted value is GM ☉ = 1.327 124 420 99 (10) × 10 20 m 3 ⋅s −2.
For most objects in the solar system, the OC echo dominates and the most commonly reported radar albedo parameter is the (normalized) OC radar albedo (often shortened to radar albedo): [84] ^ = where the denominator is the effective cross-sectional area of the target object with mean radius, r {\displaystyle r} .