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The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the scope of the Solar System and is about 3.26 light-years: 1 pc = 1 au/tan(1″) [ 6 ] [ 61 ] Proxima Centauri
One astronomical unit (au), the distance from the Sun to the Earth, is just under 5 × 10 −6 pc. The most distant space probe, Voyager 1, was 0.000 7897 pc from Earth as of February 2024. Voyager 1 took 46 years to cover that distance. The Oort cloud is estimated to be approximately 0.6 pc in diameter
1.6 × 10 0 ly: The Oort cloud is approximately two light-years in diameter. Its inner boundary is speculated to be at 50 000 au ≈ 0.8 ly, with its outer edge at 100 000 au ≈ 1.6 ly. 2.0 × 10 0 ly: Approximate maximum distance at which an object can orbit the Sun (Hill sphere/Roche sphere, 125 000 au).
an object of diameter 725.27 km at a distance of 1 astronomical unit (AU) an object of diameter 45 866 916 km at 1 light-year; an object of diameter 1 AU (149 597 871 km) at a distance of 1 parsec (pc) Thus, the angular diameter of Earth's orbit around the Sun as viewed from a distance of 1 pc is 2″, as 1 AU is the mean radius of Earth's orbit.
This is because the solar constant is evaluated at a fixed distance of 1 Astronomical Unit (au) while the solar irradiance will be affected by the eccentricity of the Earth's orbit. Its distance to the Sun varies annually between 147.1·10 6 km at perihelion and 152.1·10 6 km at aphelion.
1.079 Tm – 7.2 au – one light-hour; 1.114 Tm – 7.5 au – diameter of WOH G64, a star in the Large Magellanic Cloud, which recently transformed from a red hypergiant to a yellow hypergiant [187] 1.4 Tm – 9.5 au – average distance between Saturn and the Sun; 1.47 Tm – 9.9 au – diameter of HR 5171 A, a yellow hypergiant star. [188]
Earth (0.98–1.02 AU) [D 6] is the only place in the universe where life and surface liquid water are known to exist. [102] Earth's atmosphere contains 78% nitrogen and 21% oxygen, which is the result of the presence of life. [103] [104] The planet has a complex climate and weather system, with conditions differing drastically between climate ...
An astronomical unit (AU) is approximately the average distance between the Earth and Sun. It was redefined in 2012 as exactly 149 597 870 700 m. [99] [100] Previously the AU was not based on the International System of Units but in terms of the gravitational force exerted by the Sun in the framework of classical mechanics.