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Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. ... Earth: 0.009168 6,378 [18] Venus: 0.00869 6,051.8 [18] Mars:
Average distance from the Sun – Earth: 1.00 – Average distance of Earth's orbit from the Sun (sunlight travels for 8 minutes and 19 seconds before reaching Earth) – Mars: 1.52 – Average distance from the Sun – Jupiter: 5.2 – Average distance from the Sun – Light-hour: 7.2 – Distance light travels in one hour – Saturn: 9.5 –
Inaccuracies of these measured parameters make determining the true minimum distances of any encountering stars or brown dwarfs fairly difficult. [72] One of the first stars known to approach the Sun particularly close is Gliese 710. The star, whose mass is roughly half that of the Sun, is currently 62 light-years from the Solar System.
Star 3rd century BC — 1609 380 Earth radii (very inaccurate, true=16000 Earth radii) Aristarchus of Samos made a measurement of the distance of the Sun from the Earth in relation to the distance of the Moon from the Earth. The distance to the Moon was described in Earth radii (20, also inaccurate).
The calculated stellar distance will be in the same measurement unit as used in Distance earth-sun (e.g. if Distance earth-sun = 1 au, unit for Distance star is in astronomical units; if Distance earth-sun = 1.5813 × 10 −5 ly, unit for Distance star is in light-years).
The instantaneous lunar distance is constantly changing. The actual distance between the Moon and Earth can change as quickly as 75 meters per second, [20] or more than 1,000 km (620 mi) in just 6 hours, due to its non-circular orbit. [21] There are other effects that also influence the lunar distance. Some factors include:
Radar is used to measure the distance between the orbits of the Earth and of a second body. From that measurement and the ratio of the two orbit sizes, the size of Earth's orbit is calculated. The Earth's orbit is known with an absolute precision of a few meters and a relative precision of a few parts in 100 billion (1 × 10 −11).
The astronomical unit of length is now defined as exactly 149 597 870 700 meters. [4] It is approximately equal to the mean Earth–Sun distance. It was formerly defined as that length 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 ...