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The astronomical unit is typically used for stellar system scale distances, such as the size of a protostellar disk or the heliocentric distance of an asteroid, whereas other units are used for other distances in astronomy. The astronomical unit is too small to be convenient for interstellar distances, where the parsec and light-year are
The astronomical system of units, formerly called the IAU (1976) System of Astronomical Constants, is a system of measurement developed for use in astronomy. It was adopted by the International Astronomical Union (IAU) in 1976 via Resolution No. 1, [ 1 ] and has been significantly updated in 1994 and 2009 (see Astronomical constant ).
1 astronomical unit (au); mean distance between Earth and Sun 10 12: 1 terameter (Tm) 1.3 Tm Optical diameter of Betelgeuse: 1.4 Tm Orbital distance of Saturn from Sun 2 Tm Estimated optical diameter of VY Canis Majoris, one of the largest-known stars: 5.9 Tm Orbital distance of Pluto from the Sun ~ 7.5 Tm Outer boundary of the Kuiper belt: 10 ...
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 ...
Distances expressed in fractions of a parsec usually involve objects within a single star system. So, for example: 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.
Pages in category "Units of measurement in astronomy" ... Astronomical unit; Z. Zodi This page was last edited on 22 July 2015, at 01:17 (UTC). ...
The TU (for time unit) is a unit of time defined as 1024 μs for use in engineering. The svedberg is a time unit used for sedimentation rates (usually of proteins). It is defined as 10 −13 seconds (100 fs). The galactic year, based on the rotation of the galaxy and usually measured in million years. [2]
A more complex definition of absolute magnitude is used for planets and small Solar System bodies, based on its brightness at one astronomical unit from the observer and the Sun. The Sun has an apparent magnitude of −27 and Sirius , the brightest visible star in the night sky, −1.46.