Newcomb's Tables of the Sun (full title ''Tables of the Motion of the Earth on its Axis and Around the Sun'') is a work by the American astronomer and mathematician

Simon Newcomb Simon Newcomb (March 12, 1835 – July 11, 1909) was a Canadian–American astronomer, applied mathematician, and autodidactic polymath. He served as Professor of Mathematics in the United States Navy and at Johns Hopkins University. Born in N ...

, published in volume VI of the serial publication ''Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac''. The work contains Newcomb's mathematical development of the position of the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...

in the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

, which is constructed from classical

celestial mechanics Celestial mechanics is the branch of astronomy that deals with the motions of objects in outer space. Historically, celestial mechanics applies principles of physics (classical mechanics) to astronomical objects, such as stars and planets, ...

as well as centuries of astronomical measurements. The bulk of the work, however, is a collection of tabulated precomputed values that provide the position of the sun at any point in time. Newcomb's ''Tables'' were the basis for practically all

ephemerides In astronomy and celestial navigation, an ephemeris (pl. ephemerides; ) is a book with tables that gives the trajectory of naturally occurring astronomical objects as well as artificial satellites in the sky, i.e., the position (and possibly ...

of the Sun published from 1900 through 1983, including the annual almanacs of the U.S. Naval Observatory and the

Royal Greenwich Observatory The Royal Observatory, Greenwich (ROG; known as the Old Royal Observatory from 1957 to 1998, when the working Royal Greenwich Observatory, RGO, temporarily moved south from Greenwich to Herstmonceux) is an observatory situated on a hill in ...

. The physical tables themselves were used by the ephemerides from 1900 to 1959, computerized versions were used from 1960 to 1980, and evaluations of the Newcomb's theories were used from 1981 to 1983. (1992: p. 317) The tables are seldom used now; since the

Astronomical Almanac ''The Astronomical Almanac''The ''Astronomical Almanac'' for the Year 2015, (United States Naval Observatory/Nautical Almanac Office, 2014) . is an almanac published by the United States Naval Observatory (USNO) and His Majesty's Nautical Almanac ...

for 1984 they have been superseded by more accurate numerically-integrated ephemerides developed at

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a Federally funded research and development centers, federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, La Cañada Flintridge, California ...

, based on much more accurate observations than were available to Newcomb. Also, the tables did not account for the effects of

general relativity General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics ...

which was unknown at the time. Nevertheless, his tabulated values remain accurate to within a few seconds of arc to this day. He developed similar formulas and tables for the planets Mercury,

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus ( Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars), grandfather of Zeus (Jupiter) and father of ...

and

Neptune Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 time ...

; those of the inner planets have proved to be the most accurate.

Expressions

Certain expressions have been cited in a number of other works over a long period, and are listed below. Newcomb assigns the symbol T to the time since "1900, Jan. 0, Greenwich Mean noon", measured in Julian centuries of 36,525 days.

Sun's geometric mean longitude

The Sun's geometric mean longitude, freed from aberration is given as :L = 279° 41' 48.04" + " T + 1.089" T² Authors citing this expression include Borkowski (p. 12) and the Nautical Almanac Offices of the United Kingdom and United States (p. 98).

Fictitious mean Sun

Newcomb gives the

Right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the ( hour circle of the) point in question above the earth. When pair ...

of the fictitious mean Sun, affected by aberration (which is used in finding

mean solar time Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Two types of solar time are apparent solar time ( sundia ...

) as : τ = 18^h 38^m 45.836^s + ^s T + 0.0929^s T² Authors citing this expression include McCarthy & Seidelmann (p. 13) and the Nautical Almanac Offices of the United Kingdom and United States (p. 73).

Discontinuance

By 1970 the astronomical community recognized the need for improved ephemerides, which are used to prepare national almanacs. The changes required were * a new fundamental catalog of stars to replace FK4 * the use of improved values of astronomical constants that had been discovered * a better definition and practical realization of ephemeris time which would take advantage of atomic time * a new

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided ...

to replace 1950.0 It was decided to introduce as many changes as possible at one time in a consistent system, and the new system would go into effect for the 1984 edition of the ephemerides. "The majority of the resolutions were prepared and adopted by the General Assembly of the IAU at the 1976 and 1979 meetings." The new fundamental ephemeris was prepared by the

and named DE200/LE200. It uses

numerical integration In analysis, numerical integration comprises a broad family of algorithms for calculating the numerical value of a definite integral, and by extension, the term is also sometimes used to describe the numerical solution of differential equatio ...

.ibid., S26.

Notes

References

{{reflist

Works cited

* Borkowski, K. M
"The Tropical Year and Solar Calendar"
''Journal of the Royal Astronomical Society of Canada'' 85 no. 3 (1990): 121–130. * McCarthy, D. D. & Seidelmann, P. K. ''TIME from Earth Rotation to Atomic Physics''. (Weinheim: Wiley-VCH, 2009). * .S.Nautical Almanac Office and

HM Nautical Almanac Office His Majesty's Nautical Almanac Office (HMNAO), now part of the United Kingdom Hydrographic Office, was established in 1832 on the site of the Royal Observatory, Greenwich (ROG), where ''The Nautical Almanac'' had been published since 1767. HMNAO ...

. "The Improved IAU System", a supplement bound with ''The Astronomical Almanac for the Year 1984''. (Washington and London: U.S. Government Printing Office and Her Majesty's Stationery Office, 1983). * Nautical Almanac Offices of the United Kingdom and United States of America. ''Explanatory Supplement to the Ephemeris''. (London: Her Majesty's Stationery Office, 1961). * Newcomb, Simon.
Tables of the Four Inner Planets
', 2nd ed. (Washington: Bureau of Equipment, Navy Dept., 1898). Astronomy books