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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
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).
The largest unit for expressing distances across space at that time was the astronomical unit, equal to the radius of the Earth's orbit at 150 million kilometres (93 million miles). In those terms, trigonometric calculations based on 61 Cygni's parallax of 0.314 arcseconds, showed the distance to the star to be 660 000 astronomical units (9.9 ...
149.6 Gm (93.0 million mi; 1.0 au) – average distance between the Earth and the Sun – the original definition of the astronomical unit; 199 Gm (1.3 au) – diameter of Rho Persei, an asymptotic giant branch star, fusing carbon into neon in a shell surrounding an inert core. [179] 228 Gm (1.5 au) – distance between Mars and the Sun
The astronomical unit of mass is the solar mass. [1] The symbol M ☉ is often used to refer to this unit. The solar mass (M ☉), 1.988 92 × 10 30 kg, is a standard way to express mass in astronomy, used to describe the masses of other stars and galaxies.
The closest encounter to the Sun so far predicted is the low-mass orange dwarf star Gliese 710 / HIP 89825 with roughly 60% the mass of the Sun. [4] It is currently predicted to pass 0.1696 ± 0.0065 ly (10 635 ± 500 au) from the Sun in 1.290 ± 0.04 million years from the present, close enough to significantly disturb the Solar System's Oort ...
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.
(1.017 AU is Earth's aphelion distance.) The Amors have orbits strictly outside Earth's orbit: an Amor asteroid's perihelion distance (q) is greater than Earth's aphelion distance (1.017 AU). Amor asteroids are also near-Earth objects so q < 1.3 AU. In summary, 1.017 AU < q < 1.3 AU. (This implies that the asteroid's semi-major axis (a) is also ...