At one astronomical unit from the sun ( the Earth's distance ) the dust orbits are probably nearly circular.

However, the use of AU to refer to the astronomical unit is widespread.

The astronomical constant whose value is one astronomical unit is referred to as unit distance and is given the symbol A.

This value of the astronomical unit had to be obtained experimentally and so is was not known exactly.

The time to traverse an AU is found to be τ < sub > A </ sub > =, resulting in the astronomical unit in metres as c < sub > 0 </ sub > τ < sub > A </ sub > =.

As the speed of light in meters per second ( c < sub > 0 </ sub >) is fixed in the International System of Units, this measurement of the speed of light in AU / d ( c < sub > AU </ sub >) also determines the value of the astronomical unit in meters ( A ):

The best current ( 2009 ) estimate of the International Astronomical Union ( IAU ) for the value of the astronomical unit in meters is A = m, based on a comparison of JPL and IAA – RAS ephemerides.

With the definitions used before 2012, the astronomical unit was dependent on the heliocentric gravitational constant, that is the product of the gravitational constant G and the solar mass M < sub >☉</ sub >.

The 1976 definition of the astronomical unit was incomplete, in particular because it does not specify the frame of reference in which time is to be measured, but proved practical for the calculation of ephemerides: a fuller definition that is consistent with general relativity was proposed, and " vigorous debate " ensued until in August 2012 the International Astronomical Union adopted the current definition of 1 astronomical unit = 149597870700 meters.

In this case, the absolute magnitude is defined as the apparent magnitude that the object would have if it were one astronomical unit ( AU ) from both the Sun and the observer.

Following this, an astronomical conference held in Paris in 1950 recommended " that in all cases where the mean solar second is unsatisfactory as a unit of time by reason of its variability, the unit adopted should be the sidereal year at 1900. 0, that the time reckoned in this unit be designated ephemeris time ", and gave Clemence's formula ( see Definition of ephemeris time ( 1952 )) for translating mean solar time to ephemeris time.

The scale is in astronomical unit s. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.

Units used to denote distances in the vastness of space, as in astronomy, are much longer than those typically used on Earth and include the astronomical unit, the light-year, and the parsec.

In old astronomical texts, minute can also mean a unit of time equal to of a day ( 24 usual minutes ).

If viewed from a distance of 1 astronomical unit, it would span an angular diameter of 35 ° and shine at magnitude − 38.

The term ephemeris time ( often abbreviated ET ) can in principle refer to time in connection with any astronomical ephemeris.

Right ascension ( abbreviated RA ; symbol α ) is the astronomical term for one of the two direction coordinates of a point on the celestial sphere in the equatorial coordinate system, usually combined with declination.

The High Energy Transient Explorer ( abbreviated HETE ; also known as Explorer 79 ) was an American astronomical satellite with international participation ( mainly Japan and France ).

The " Apparent Places of Fundamental Stars " ( commonly abbreviated APFS ) is an astronomical yearbook, which is published one year in advance by the Astronomisches Rechen-Institut in Heidelberg, Germany.

In 1976 the International Astronomical Union ( IAU ) revised the definition of the AU for greater precision, defining it as that length for which the Gaussian gravitational constant ( k ) takes the value when the units of measurement are the astronomical units of length, mass and time.

The comparison of the ephemeris with the measured positions leads to a value for the speed of light in astronomical units, which is AU / d ( TDB ).

The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit ( AU ) ( roughly the mean distance from the Sun to the Earth ).

The resulting values can be divided by 10 to convert them into astronomical units ( AU ), which would result in the expression

At the measured distance of Vega, this corresponded to an actual radius of 80 astronomical units ( AU ), where an AU is the average radius of the Earth's orbit around the Sun.

* 149. 6 Gm ( 93. 0 million mi ) — 1. 0 AU — Distance between the Earth and the Sun-the definition of the astronomical unit

To help compare different distances this page lists lengths starting at 10 < sup > 15 </ sup > m ( 1 Pm or 1, 000, 000 million km or 6685 astronomical units ( AU ) or 0. 11 light years ).

The astronomical measurements taken of the transit of Venus by a number of countries since 1639 resulted in a progressively more accurate definition of the AU.

In the Crab Nebula X-ray spectrum there are three features that differ greatly from Scorpius X-1: its spectrum is much harder, its source diameter is in light-years ( ly ) s, not astronomical units ( AU ), and its radio and optical synchrotron emission are strong.

The estimated semi-major axis of the planet's orbit is 1. 2 astronomical units ( AU ), which would give it a periapsis distance of 0. 9 AU and an apoapsis distance of 1. 5 AU.

It was approximately 2 astronomical units ( AU ) from the Sun.

Current data indicate that this planet orbits with a period of about 7 years at a mean separation of 3. 4 astronomical units ( AU ), where 1 AU is the mean distance between the Earth and the Sun.

The orbital radius at which the stellar flux from Epsilon Eridani matches the solar constant — where the emission matches the Sun's output at the orbital distance of the Earth — is 0. 61 astronomical units ( AU ).

Based upon the length of the year, the distance from the Earth to the Sun ( an astronomical unit or AU ), and the gravitational constant ( G ), the mass of the Sun is given by:

Its orbital period changed from 43 years to about 6 years, and its perihelion is now about 1. 59 AU ( astronomical unit ).

" or " au ", not to be confused with the same abbreviation used also for astronomical units, arbitrary units, and absorbance units in different contexts.

Solving astronomical problems requires, for Copernicus, not a random search of unrelated tables, but a regular employment of the rules defining the entire discipline.

therefore, only with precise foreknowledge of the line frequencies is an astronomical search for the radio spectra of these molecules feasible.

After an unspeakable siege, lasting the better part of two months, it was announced that the studio `` owed '' the government a tax debt in excess of eight million dollars while I, who had always remained aloof from such iniquitous practices as paying taxes on the salary I had earned and the little I legally inherited as Morris' helpless relict, was `` stung '' with a personal bill of such astronomical proportions as to `` wipe out '' all but a fraction of my poor, hard-come-by savings.

Numbers would be astronomical and current fiscal policies make this an impractical solution.

The expense and time involved are astronomical.

It is the basis for Coordinated Universal Time ( UTC ), which is used for civil timekeeping all over the Earth's surface, and for Terrestrial Time, which is used for astronomical calculations.

This synchronisation was inevitably imperfect, depending as it did on the astronomical realisation of UT2.

A range of astronomy software is available and used by amateur astronomers, including software that generates maps of the sky, software to assist with astrophotography, observation scheduling software, and software to perform various calculations pertaining to astronomical phenomena.

With more advanced equipment, but still cheap in comparison to professional setups, amateur astronomers can measure the light spectrum emitted from astronomical objects, which can yield high-quality scientific data if the measurements are performed with due care.

There is a large number of amateur astronomical societies around the world that serve as a meeting point for those interested in amateur astronomy, whether they be people who are actively interested in observing or " armchair astronomers " who may simply be interested in the topic.

* Andrew Ainslie Common ( 1841 – 1903 ), built his own very large reflecting telescopes and demonstrated that photography could record astronomical features invisible to the human eye.

These terms have historically been applied to any astronomical object orbiting the Sun that did not show the disk of a planet and was not observed to have the characteristics of an active comet, but as small objects in the outer Solar System were discovered, their volatile-based surfaces were found to more closely resemble comets, and so were often distinguished from traditional asteroids.

They are grouped with the outer bodies — centaurs, Neptune trojans, and trans-Neptunian objects — as minor planets, which is the term preferred in astronomical circles.

Many Chacoan buildings may have been aligned to capture the solar and lunar cycles, requiring generations of astronomical observations and centuries of skillfully coordinated construction.

Furthermore, considering that some of these roads seem to go nowhere, experts suggest that they can be linked — especially the Great North Road — to astronomical observations, solstice marking, and agricultural cycles.

Chacoan and other structures constructed originally along astronomical alignments, and thought to have served important ceremonial purposes to the culture, were systematically dismantled.

Astrographs using astronomical photographic plates sped the process in the early 20th century.

In astronomy, a given point on the celestial sphere ( that is, the apparent position of an astronomical object ) can be identified using any of several astronomical coordinate systems, where the references vary according to the particular system.