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The 1976 definition of the astronomical unit was incomplete because it did not specify the frame of reference in which to apply the measurement, but proved practical for the calculation of ephemerides: a fuller definition that is consistent with general relativity was proposed, [26] and "vigorous debate" ensued [27] until August 2012 when the ...
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 ...
A unit of length used to express astronomical distances that is equivalent to the distance that an object moving at the speed of light in vacuum would travel in one Julian year: approximately 9.46 trillion kilometres (9.46 × 10 12 km) or 5.88 trillion miles (5.88 × 10 12 mi).
The astronomical unit of length is known as the astronomical unit (A or au), which in the IAU(1976) system is defined as the length for which the gravitational constant, more specifically the Gaussian gravitational constant k expressed in the astronomical units (i.e. k 2 has units A 3 S −1 D −2), takes the value of 0.017 202 098 95. This ...
It has been a central subject for astronomical research since antiquity. The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years. From Earth, it is 1 astronomical unit (1.496 × 10 8 km) or about 8 light-minutes away. Its diameter is about 1,391,400 km (864,600 mi), 109 times that of Earth.
The numbers refer to astronomical units, the mean distance between Sun and Earth, which is 1.496 × 10 8 km (93 × 10 6 miles). The Derby Orrery does not show mean distance, but demonstrated the relative planetary movements.
A contemporary German popular astronomical book also noticed that light-year is an odd name. [25] In 1868 an English journal labelled the light-year as a unit used by the Germans. [26] Eddington called the light-year an inconvenient and irrelevant unit, which had sometimes crept from popular use into technical investigations. [27]
A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (not to scale). 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).