In 1976 the IAU resolved that the theoretical basis for its current ( 1952 ) standard of Ephemeris Time was non-relativistic, and that therefore, beginning in 1984, Ephemeris Time would be replaced by two relativistic timescales intended to constitute dynamical timescales: Terrestrial Dynamical Time ( TDT ) and Barycentric Dynamical Time ( TDB ).

Ten years after the Solvay conference, at the plenary session of the IAU in Prague, the well-known American astronomer Alan Sandage said, “ today, no astronomer would deny the mystery surrounding the nuclei of galaxies or that the first to recognize the rich reward held in this treasury was Viktor Ambartsumian .”

Benjamin Zimmer of Language Log summarised the confusion: " The fact that the IAU would like us to think of dwarf planets as distinct from ' real ' planets lumps the lexical item ' dwarf planet ' in with such oddities as ' Welsh rabbit ' ( not really a rabbit ) and ' Rocky Mountain oysters ' ( not really oysters ).

The IAU also recommends values in SI units, which are the values which would be measured ( in proper length and proper time ) by an observer at the barycentre of the Solar System: these are obtained by the following transformations:

Today the IAU does not recognise the name Mare Desiderii.

With an old Spitzer size estimate of, it was a dwarf planet candidate ( icy trans-Neptunian objects with a diameter above around 400 km are expected to be spherical ) although the IAU has never classified it as such.

This came to a head at a meeting sponsored by the IAU in Oxford in 1981.

Brian Marsden, the head of the Minor Planet Center, said that such an action was a violation of protocol, and that some members of the IAU might vote against it.

Although there are only 88 IAU constellations, the sky is actually divided into 89 irregularly shaped boxes as the constellation Serpens is split into two separate sections, Serpens Caput ( the snake's head ) to the west and Serpens Cauda ( the snake's tail ) to the east.

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.

* Strasbourg Astronomical Data Center Files on official IAU constellation boundaries

After it was shown that at least one such body was larger than Pluto, on August 24, 2006 the International Astronomical Union ( IAU ) reclassified Pluto, grouping it with two similarly sized " dwarf planets " rather than with the eight " classical planets ".

The discovery was announced in IAU Circular 5725 on March 27, 1993.

Two impact craters on Olympus Mons have been assigned provisional names by the IAU.

Named features on bodies so small that coordinates have not yet been determined are identified on drawings of the body that are included in the IAU Transactions volume of the year when the names were adopted.

* IAU FAQ on " Naming Stars "

TT was formally defined in terms of Geocentric Coordinate Time ( TCG ), defined by the IAU on the same occasion.

" Report of the IAU WGAS Sub-group on Numerical Standards ".

The International Astronomical Union ( IAU ) defines the north pole as that which lies on the north side of the invariable plane of the Solar System ; under this system Venus ' tilt is 3 °, it rotates retrograde, and the right hand rule does not apply.

The IAU nomenclature standards have stated that features on Phoebe are to be named after characters in the Greek myth of Jason and the Argonauts.

In 1988, the International Astronomical Union's Working Group for Planetary System Nomenclature ( IAU / WGPSN ) officially adopted the name Inuvik for a crater on Mars, at 78. 7 ° north latitude and 28. 6 ° west longitude.

* United States Naval Observatory Circular 179: The IAU Resolutions on Astronomical Reference Systems, Time Scales, and Earth Rotation Models Explanation and Implementation

* Bracewell, Ronald N., ed., Paris Symposium on Radio Astronomy, IAU Symposium no.

In 1976, the International Astronomical Union's Working Group for Planetary System Nomenclature ( IAU / WGPSN ) officially adopted the name Banff for a crater on Mars, after the town in Alberta.

For example, the Sun enters the IAU boundary of Aries on April 19 at the lower right corner, a position that is still rather closer to the " body " of Pisces than of Aries.

On February 2, 2004 the astronauts on Space Shuttle Columbia's final mission were further memorialized when NASA named a set of hills to the east of the landing site the Columbia Hills Complex, denoting seven peaks in that area as " Anderson ", " Brown ", " Chawla ", " Clark ", " Husband ", " McCool ", and " Ramon "; NASA has submitted these geographical feature names to the IAU for approval.

Of the latter constellations, only Camelopardalis and Monoceros are still found on modern star charts, and recognized by the IAU.

On March 23, 2009, Brown asked readers of his weekly column to suggest possible names for the satellite, with the best one to be submitted to the International Astronomical Union ( IAU ) on April 5.

He developed the ephemeris time scale, which had been adopted by the IAU in 1952 on a proposal formulated by Clemence in 1948, as an international time standard.

He served as President of the IAU commission on time from 1955 to 1961, and was active in the International Union of Geodesy and Geophysics, the American Geophysical Union, and the International Consultative Committee for the Definition of the Second.

In 1930, the boundaries of these constellations were fixed by Eugène Joseph Delporte and adopted by the IAU, so that now every point on the celestial sphere belongs to a particular constellation.

* IAU on Naming Astronomical Objects

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.

Furthermore, it was subject to relativity and thus was not constant for all observers, therefore, in 2012, the IAU redefined it again to just simply be.

There are 88 standard constellations recognized by the International Astronomical Union ( IAU ) since 1922.

There are also numerous historical constellations not recognized by the IAU, or constellations recognized in regional traditions of astronomy or astrology, such as Chinese, Hindu and Australian Aboriginal.

For example, the asterism known as the Big Dipper corresponds to the seven brightest stars of the larger IAU constellation of Ursa Major.

In 1922, Henry Norris Russell aided the IAU in dividing the celestial sphere into 88 official constellations.

* IAU: The Constellations, including high quality maps.

The official definition of " planet " used by the International Astronomical Union ( IAU ) only covers the Solar System and thus does not apply to exoplanets.

As of April 2011, the only definitional statement issued by the IAU that pertains to exoplanets is a working definition issued in 2001 and modified in 2003.

The Extrasolar Planets Encyclopaedia includes objects up to 25 Jupiter masses, saying, " The fact that there is no special feature around 13 MJup in the observed mass spectrum reinforces the choice to forget this mass limit ," and the Exoplanet Data Explorer includes objects up to 24 Jupiter masses with the advisory: " The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to the sin i ambiguity.

They note that under these two proposed rules all of the present names for 99 % of the planets around single stars are preserved as informal forms of the IAU sanctioned provisional standard.

But the International Astronomical Union ( IAU ) currently has no plans to assign names of this sort to extrasolar planets, considering it impractical.

# a former standard astronomical time scale adopted in 1952 by the IAU, and superseded in the 1970s.

Although not an IAU standard, the ephemeris time argument T < sub > eph </ sub > has been in use at that institution since the 1960s.

The time scale represented by T < sub > eph </ sub > has been characterized as a relativistic coordinate time that differs from Terrestrial Time only by small periodic terms with an amplitude not exceeding 2 milliseconds of time: it is linearly related to, but distinct ( by an offset and constant rate which is of the order of 0. 5 sec / yr ) from the TCB time scale adopted in 1991 as a standard by the IAU.

As of 2008, only five objects in the Solar System, Ceres, Eris, and the KBOs Pluto, Makemake and Haumea, are listed as dwarf planets by the IAU.

In 2006, the International Astronomical Union ( IAU ) officially adopted a resolution defining planets within the Solar System.

Under IAU definitions, there are eight planets in the Solar System.

Names adopted by the IAU must follow various rules and conventions established and amended through the years by the Union.