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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 ...
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).
In terms of this speed, the old definition of the astronomical unit of length had the accepted value: [3] 1 au = c 0 τ A = (149 597 870 700 ± 3) m, where τ A is the transit time of light across the astronomical unit. The astronomical unit of length was determined by the condition that the measured data in the ephemeris match observations ...
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 ...
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]
In science and technology, an arbitrary unit (abbreviated arb. unit, [1] see below) or procedure defined unit [2] (p.d.u.) is a relative unit of measurement to show the ratio of amount of substance, intensity, or other quantities, to a predetermined reference measurement. The reference measurement is typically defined by the local laboratories ...
Atomic units, a system of units convenient for atomic physics and other fields; Ångström unit, a unit of length equal to 10 −10 m or 0.1 nanometre. Astronomical unit, a unit of length used in planetary systems astronomy; Arbitrary unit, a placeholder unit for when the actual value of a measurement is unknown or unimportant
Astronomical Observatory, New South Wales, Australia 1873. Astronomy (from the Greek ἀστρονομία from ἄστρον astron, "star" and -νομία -nomia from νόμος nomos, "law" or "culture") means "law of the stars" (or "culture of the stars" depending on the translation).