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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). This means that the approximately circular disc of the Earth, as viewed from the Sun, receives a roughly stable 1361 W/m 2 at all times.
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 ...
3.261 56 ly. The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles). [a] The parsec unit is obtained by the use of parallax and trigonometry ...
This is because the distance between Earth and the Sun is not fixed (it varies between 0.983 289 8912 and 1.016 710 3335 au) and, when Earth is closer to the Sun , the Sun's gravitational field is stronger and Earth is moving faster along its orbital path. As the metre is defined in terms of the second and the speed of light is constant for all ...
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.
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]
Approximate light signal travel times; Distance: Time: one foot: 1.0 ns: one metre: 3.3 ns: from geostationary orbit to Earth: 119 ms: the length of Earth's equator: 134 ms: from Moon to Earth: 1.3 s: from Sun to Earth (1 AU) 8.3 min: one light-year: 1.0 year: one parsec: 3.26 years: from the nearest star to Sun (1.3 pc) 4.2 years: from the ...
They arrived at a figure for the solar parallax of 9.5 arcseconds, [Note 1] equivalent to an Earth–Sun distance of about 22,000 Earth radii. [Note 2] They were also the first astronomers to have access to an accurate and reliable value for the radius of Earth, which had been measured by their colleague Jean Picard in 1669 as 3,269,000 toises.