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Fundamental ephemeris

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A fundamental ephemeris of the Solar System is a model of the objects of the system in space, with all of their positions and motions accurately represented. It is intended to be a high-precision primary reference for prediction and observation of those positions and motions, and which provides a basis for further refinement of the model. It is generally not intended to cover the entire life of the Solar System; usually a short-duration time span, perhaps a few centuries, is represented to high accuracy. Some long ephemerides cover several millennia to medium accuracy.

They are published by the Jet Propulsion Laboratory as Development Ephemeris. The latest releases include DE430 which covers planetary and lunar ephemeris from Dec 21, 1549 to Jan 25, 2650 with high precision and is intended for general use for modern time periods . DE431 was created to cover a longer time period Aug 15, -13200 to March 15, 17191 with slightly less precision for use with historic observations and far reaching forecasted positions. DE432 was released as a minor update to DE430 with improvements to the Pluto barycenter in support of the New Horizons mission.

Description

The set of physical laws and numerical constants used in the calculation of the ephemeris must be self-consistent and precisely specified. The ephemeris must be calculated strictly in accordance with this set, which represents the most current knowledge of all relevant physical forces and effects. Current fundamental ephemerides are typically released with exact descriptions of all mathematical models, methods of computation, observational data, and adjustment to the observations at the time of their announcement. This may not have been the case in the past, as fundamental ephemerides were then computed from a collection of methods derived over a span of decades by many researchers.

The independent variable of the ephemeris is always time. In the case of the most current ephemerides, it is a relativistic coordinate time scale equivalent to the IAU definition of TCB. In the past, mean solar time (before the discovery of the non-uniform rotation of the Earth) and ephemeris time (before the implementation of relativistic gravitational equations) were used. The remainder of the ephemeris can consist of either the mathematical equations and initial conditions which describe the motions of the bodies of the Solar System, of tabulated data calculated from those equations and conditions, or of condensed mathematical representations of the tabulated data.

A fundamental ephemeris is the basis from which apparent ephemerides, phenomena, and orbital elements are computed for astronomical, nautical, and surveyors' almanacs. Apparent ephemerides give positions and motions of Solar System bodies as seen by observers from the surface of Earth, and are useful for astronomers, navigators, and surveyors in planning observations and in reducing the data acquired, although much of the work of latter two has been supplanted by GPS technology. Phenomena are events related to the configurations of Solar System bodies, for instance rise and set times, phases, eclipses and occultations, and have many civil and scientific applications. Orbital elements are descriptions of the motion of a body at a particular instant, used for further short-time-span calculation of the body's position when high accuracy is not required.

History

Astronomers have been tasked with computing accurate ephemerides, originally for purposes of sea navigation, from at least the 18th century. In England, Charles II founded the Royal Observatory in 1675, which began publishing The Nautical Almanac in 1766. In France, the Bureau des Longitudes was founded in 1795 to publish the Connaissance des Temps. The early fundamental ephemerides of these publications came from many different sources and authors as the science of celestial mechanics matured.

At the end of the 19th century, the analytical methods of general perturbations reached the probable limits of what could be accomplished by hand calculation. The planetary "theories" of Newcomb and Hill formed the fundamental ephemerides of the Nautical Almanac at that time. For the Sun, Mercury, Venus, and Mars, the tabulations of the Astronomical Almanac continued to be derived from the work of Newcomb and Ross through 1983. In France, the works of LeVerrier and Gaillot formed the fundamental ephemeris of the Connaissance des Temps.

From the mid 20th century, work began on numerical integration of the equations of motion on early computing machines for purposes of producing fundamental ephemerides for the Astronomical Almanac. Jupiter, Saturn, Uranus, Neptune, and Pluto were based on the work of Eckert, et al. and Clemence through 1983. The fundamental ephemeris of the Moon, always a difficult problem in celestial mechanics, remained a work-in-progress through the early 1980s. It was based originally on the work of Brown, with updates and corrections by Clemence, et al. and Eckert, et al.

Starting in 1984, a revolution in the methods of producing fundamental ephemerides began. From 1984 through 2002, the fundamental ephemeris of the Astronomical Almanac was the Jet Propulsion Laboratory's DE200/LE200, a fully numerically-integrated ephemeris fitted to modern position and velocity observations of the Sun, Moon, and planets. From 2003 onward (as of Feb 2012), JPL's DE405/LE405, an integrated ephemeris referred to the International Celestial Reference Frame, has been used. In France, the Bureau des Longitudes began using their machine-generated semi-analytical theory VSOP82 in 1984, and their work continued with the founding of the Institut de mécanique céleste et de calcul des éphémérides in 1998 and the INPOP series of numerical ephemerides. DE405/LE405 were superseded by DE421/LE421 in 2008.

See also

References and notes

  1. Folkner (April 30, 2014). "JPL Memo IOM 392R-14-003" (PDF).
  2. See, for instance, Standish (1998). "JPL Planetary and Lunar Ephemerides DE405/LE405" (PDF). Archived from the original (PDF) on 2012-02-20.; Fienga; et al. (2010). "INPOP10a" (PDF).; Pitjeva (2004). "High-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants" (PDF). Archived from the original (PDF) on 2008-10-31.
  3. ^ Standish and Williams (2010). "CHAPTER 8: Orbital Ephemerides of the Sun, Moon, and Planets" (PDF). A chapter from an as-yet-unpublished (Feb 2012) version of the Explanatory Supplement (see Sources)
  4. "History of the Royal Observatory, Greenwich". 14 September 2015.
  5. "History of The Nautical Almanac". Archived from the original on 2009-06-18. Retrieved 2012-02-10.
  6. "History of the IMCCE". Archived from the original on 2012-02-27. Retrieved 2012-02-10.
  7. See Explanatory Supplement (1961), chap. 7 or Explanatory Supplement (1992), chap. 13 for extensive lists of sources of the early fundamental ephemerides of the Nautical Almanac. (see Sources)
  8. Newcomb (1898). "Tables of the Motion of the Earth on its Axis and Around the Sun". Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac. VI (Part I). U.S. Government Printing Office, Washington, DC.
  9. Newcomb (1898). "Tables of the Heliocentric Motion of Mercury". Astronom. Papers American Ephem. VI, part II (2): 171. Bibcode:1898USNAO...6..171N.
  10. Newcomb (1898). "Tables of the Heliocentric Motion of Venus". Astronom. Papers American Ephem. VI, part III: 271. Bibcode:1898USNAO...6..271N.
  11. Newcomb (1898). "Tables of the Heliocentric Motion of Mars". Astronom. Papers American Ephem. VI, part IV (4): 383. Bibcode:1898USNAO...6..383N.
  12. Newcomb (1898). "Tables of the Heliocentric Motion of Uranus". Astronom. Papers American Ephem. VII: 1. Bibcode:1898USNAO...7R...1N.
  13. Newcomb (1898). "Tables of the Heliocentric Motion of Neptune". Astronom. Papers American Ephem. VII: 1. Bibcode:1898USNAO...7Q...1N.
  14. Hill (1898). "Tables of Jupiter". Astronom. Papers American Ephem. VII.
  15. Hill (1898). "Tables of Saturn". Astronom. Papers American Ephem. VII.
  16. Ross (1917), New Elements of Mars, Astronom. Papers American Ephem., vol. IX
  17. LeVerrier (1858). "Théorie et Tables du Mouvement Apparent du Soleil". Annales de l'Observatoire Impérial de Paris (in French). IV.
  18. LeVerrier (1859). "Théorie et Tables du Mouvement de Mercure". Annales de l'Observatoire Impérial de Paris (in French). V.
  19. LeVerrier (1861). "Théorie et Tables du Mouvement de Vénus". Annales de l'Observatoire Impérial de Paris, Mémoires (in French). VI.
  20. LeVerrier (1861). "Théorie et Tables du Mouvement de Mars". Annales de l'Observatoire Impérial de Paris, Mémoires (in French). VI.
  21. LeVerrier developed and published his original theories of the outer planets in Annales de l'Observatoire de Paris, Mémoires |volume=X-|volume=XIV
  22. Gaillot (1913). "Tables Rectifiées du Mouvement de Jupiter". Annales de l'Observatoire de Paris, Mémoires (in French). XXXI.
  23. Gaillot (1904). "Tables Rectifiées du Mouvement de Saturne". Annales de l'Observatoire de Paris, Mémoires (in French). XXIV.
  24. Gaillot (1910). "Tables Nouvelles des Mouvements d'Uranus et de Neptune". Annales de l'Observatoire de Paris, Mémoires (in French). XXVIII.
  25. Eckert; Brouwer; Clemence (1951), Coordinates of the Five Outer Planets 1953–2060, Astronom. Papers American Ephem., vol. XII
  26. Clemence (1954), Perturbations of the Five Outer Planets by the Four Inner Ones, Astronom. Papers American Ephem., vol. XIII
  27. Brown (1919). Tables of the Motion of the Moon. Yale University Press, New Haven, CT.
  28. Clemence, G. M; Porter, J. G; Sadler, D. H (1952). "Aberration in the Lunar Ephemeris". Astronomical Journal. 57: 46–47. Bibcode:1952AJ.....57...46C. doi:10.1086/106703.
  29. Eckert, W. J; Walker, M. J; Eckert, D (1966). "Transformation of the Lunar Coordinates and Orbital Parameters". Astronomical Journal. 71: 314–332. Bibcode:1966AJ.....71..314E. doi:10.1086/109923.
  30. Eckert, W. J; Van Flandern, T. C; Wilkins, G. A (1969). "A Note on the Evaluation of the Latitude of the Moon". Monthly Notices of the Royal Astronomical Society. 146 (4): 473–478. Bibcode:1969MNRAS.146..473E. doi:10.1093/mnras/146.4.473.
  31. See also Nautical Almanac Office, U.S. Naval Observatory; H.M. Nautical Almanac Office, Royal Greenwich Observatory (1954), Improved Lunar Ephemeris, U.S. Government Printing Office, Washington, DC.
  32. See Newhall, X. X; Standish, E. M; Williams, J. G (1983). "DE 102 – A numerically integrated ephemeris of the moon and planets spanning forty-four centuries". Astronomy and Astrophysics. 125 (1): 150. Bibcode:1983A&A...125..150N. for a good description of the new methods from their early days.
  33. Bretagnon, P (1982). "Théorie du mouvement de l'ensemble des planètes. Solution VSOP82". Astronomy and Astrophysics (in French). 114: 278. Bibcode:1982A&A...114..278B.
  34. Fienga; et al. (2006). "INPOP06. A new numerical planetary ephemeris" (PDF).; Fienga; et al. (2008). "INPOP08, a 4-D planetary ephemeris" (PDF).; Fienga; et al. (2010). "INPOP10a" (PDF).
  35. INPOP17a planetary ephemerides (PDF). Institut de mécanique céleste et de calcul des éphémérides. 2017. ISBN 978-2-910015-79-4.
  36. Folkner, William (April 30, 2014). "JPL Planetary and Lunar Ephemerides".

Sources

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