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Total solar irradiance (TSI) is a measure of the solar power over all wavelengths per unit area incident on the Earth's upper atmosphere. It is measured perpendicular to the incoming sunlight. [3] The solar constant is a conventional measure of mean TSI at a distance of one astronomical unit (AU).
Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun 's photosphere where the optical depth equals 2/3: [1] 695,700 kilometres (432,300 miles) is approximately 10 times the average radius of Jupiter, 109 times the radius ...
Earth's orbit. Earth orbits the Sun at an average distance of 149.60 million km (92.96 million mi), or 8.317 light-minutes, [1] in a counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes 365.256 days (1 sidereal year), during which time Earth has traveled 940 million km (584 million mi). [2]
The solar constant includes radiation over the entire electromagnetic spectrum. It is measured by satellite as being 1.361 kilo watts per square meter (kW/m 2) at solar minimum (the time in the 11-year solar cycle when the number of sunspots is minimal) and approximately 0.1% greater (roughly 1.362 kW/m 2) at solar maximum.
This means that the Sun is (a mean of) 6 + 3 ⁄ 4 times wider than the Earth, or that the Sun is 13 + 1 ⁄ 2 Earth-radii wide. The Moon and Sun must then be 20 + 1 ⁄ 4 and 387 Earth-radii away from us in order to subtend an angular size of 2º.
Approximate maximum distance at which an object can orbit the Sun (Hill sphere/Roche sphere, 125 000 au). Beyond this is the deep ex-solar gravitational interstellar medium. 4.24 × 10 0 ly: The nearest known star (other than the Sun), Proxima Centauri, is about 4.24 light-years away. [31] [32] 8.6 × 10 0 ly: Sirius, the brightest star of the ...
The Sun is a weakly variable star, and its actual luminosity therefore fluctuates. [3] The major fluctuation is the eleven-year solar cycle (sunspot cycle) that causes a quasi-periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much smaller than this. [4]
Since the surface area of a sphere of radius r is A = 4πr 2, the intensity I (power per unit area) of radiation at distance r is = =. The energy or intensity decreases (divided by 4) as the distance r is doubled; if measured in dB would decrease by 6.02 dB per doubling of distance. When referring to measurements of power quantities, a ratio ...