Fundamental ephemeris

Last updated

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.

Contents

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. [1]

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. [2] 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. [3]

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. [3] 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, [4] which began publishing The Nautical Almanac in 1766. [5] In France, the Bureau des Longitudes was founded in 1795 to publish the Connaissance des Temps . [6] The early fundamental ephemerides of these publications came from many different sources and authors as the science of celestial mechanics matured. [7]

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 [8] [9] [10] [11] [12] [13] and Hill [14] [15] 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 [16] through 1983. In France, the works of LeVerrier [17] [18] [19] [20] [21] and Gaillot [22] [23] [24] 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. [25] and Clemence [26] 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, [27] with updates and corrections by Clemence, et al. [28] and Eckert, et al. [29] [30] [31]

Starting in 1984, a revolution in the methods of producing fundamental ephemerides began. [32] 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. [3] In France, the Bureau des Longitudes began using their machine-generated semi-analytical theory VSOP82 in 1984, [33] and their work continued with the founding of the Institut de mécanique céleste et de calcul des éphémérides in 1998 and the INPOP [34] [35] series of numerical ephemerides. DE405/LE405 were superseded by DE421/LE421 in 2008. [36]

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. 1 2 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

Related Research Articles

<span class="mw-page-title-main">Astronomical unit</span> Mean distance between Earth and the Sun

The astronomical unit is a unit of length defined to be exactly equal to 149,597,870,700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance, before its modern redefinition in 2012.

Δ<i>T</i> (timekeeping) Measure of variation of solar time from atomic time

In precise timekeeping, ΔT is a measure of the cumulative effect of the departure of the Earth's rotation period from the fixed-length day of International Atomic Time. Formally, ΔT is the time difference ΔT = TT − UT between Universal Time and Terrestrial Time. The value of ΔT for the start of 1902 was approximately zero; for 2002 it was about 64 seconds. So Earth's rotations over that century took about 64 seconds longer than would be required for days of atomic time. As well as this long-term drift in the length of the day there are short-term fluctuations in the length of day which are dealt with separately.

<span class="mw-page-title-main">Ecliptic</span> Apparent path of the Sun on the celestial sphere

The ecliptic or ecliptic plane is the orbital plane of Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic against the background of stars. The ecliptic is an important reference plane and is the basis of the ecliptic coordinate system.

The term ephemeris time can in principle refer to time in association with any ephemeris. In practice it has been used more specifically to refer to:

  1. a former standard astronomical time scale adopted in 1952 by the IAU, and superseded during the 1970s. This time scale was proposed in 1948, to overcome the disadvantages of irregularly fluctuating mean solar time. The intent was to define a uniform time based on Newtonian theory. Ephemeris time was a first application of the concept of a dynamical time scale, in which the time and time scale are defined implicitly, inferred from the observed position of an astronomical object via the dynamical theory of its motion.
  2. a modern relativistic coordinate time scale, implemented by the JPL ephemeris time argument Teph, in a series of numerically integrated Development Ephemerides. Among them is the DE405 ephemeris in widespread current use. The time scale represented by Teph is closely related to, but distinct from, the TCB time scale currently adopted as a standard by the IAU.
<span class="mw-page-title-main">Ecliptic coordinate system</span> Celestial coordinate system used to describe Solar System objects

In astronomy, the ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the March equinox, and it has a right-hand convention. It may be implemented in spherical or rectangular coordinates.

<span class="mw-page-title-main">Axial tilt</span> Angle between the rotational axis and orbital axis of a body

In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbital plane. It differs from orbital inclination.

In astronomy and celestial navigation, an ephemeris 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 over time. Historically, positions were given as printed tables of values, given at regular intervals of date and time. The calculation of these tables was one of the first applications of mechanical computers. Modern ephemerides are often provided in electronic form. However, printed ephemerides are still produced, as they are useful when computational devices are not available.

<span class="mw-page-title-main">Urbain Le Verrier</span> French astronomer and mathematician (1811–1877)

Urbain Jean Joseph Le Verrier was a French astronomer and mathematician who specialized in celestial mechanics and is best known for predicting the existence and position of Neptune using only mathematics.

Barycentric Dynamical Time is a relativistic coordinate time scale, intended for astronomical use as a time standard to take account of time dilation when calculating orbits and astronomical ephemerides of planets, asteroids, comets and interplanetary spacecraft in the Solar System. TDB is now defined as a linear scaling of Barycentric Coordinate Time (TCB). A feature that distinguishes TDB from TCB is that TDB, when observed from the Earth's surface, has a difference from Terrestrial Time (TT) that is about as small as can be practically arranged with consistent definition: the differences are mainly periodic, and overall will remain at less than 2 milliseconds for several millennia.

Newcomb's Tables of the Sun is a work by the American astronomer and mathematician Simon Newcomb, 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 in the Solar System, which is constructed from classical celestial mechanics 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.

<span class="mw-page-title-main">36 Atalante</span> Main-belt asteroid

Atalante is a large, dark main-belt asteroid. It was discovered by the German-French astronomer H. Goldschmidt on October 5, 1855, and named by French mathematician Urbain Le Verrier after the Greek mythological heroine Atalanta. It was rendered 'Atalanta' in English sources in the 19th century. This asteroid is classified as C-type (carbonaceous), according to the Tholen classification system.

<span class="mw-page-title-main">Ernest William Brown</span> English-American astronomer and mathematician (1866–1938)

Ernest William Brown FRS was an English mathematician and astronomer, who spent the majority of his career working in the United States and became a naturalised American citizen in 1923.

Aurelia is a main-belt asteroid that was discovered by German astronomer Max Wolf on September 7, 1896, in Heidelberg. It is classified as an F-type asteroid.

Lunar theory attempts to account for the motions of the Moon. There are many small variations in the Moon's motion, and many attempts have been made to account for them. After centuries of being problematic, lunar motion can now be modeled to a very high degree of accuracy.

Richard Dunthorne was an English astronomer and surveyor, who worked in Cambridge as astronomical and scientific assistant to Roger Long, and also concurrently for many years as surveyor to the Bedford Level Corporation.

The Astronomical Almanac is an almanac published by the United Kingdom Hydrographic Office; it also includes data supplied by many scientists from around the world. On page vii, the listed major contributors to its various Sections are: H.M Nautical Almanac Office, United Kingdom Hydrographic Office; the Nautical Almanac Office, United States Naval Observatory; the Jet Propulsion Laboratory, California Institute of Technology; the IAU Standards Of Fundamental Astronomy (SOFA) initiative; the Institut de Mécanique Céleste et des Calcul des Éphémerides, Paris Observatory; and the Minor Planet Center, Cambridge, Massachusetts. It is considered a worldwide resource for fundamental astronomical data, often being the first publication to incorporate new International Astronomical Union resolutions. The almanac largely contains Solar System ephemerides based on the JPL Solar System integration "DE440", and catalogs of selected stellar and extragalactic objects. The material appears in sections, each section addressing a specific astronomical category. The book also includes references to the material, explanations, and examples. It used to be available up to one year in advance of its date, however the current 2024 edition became available only one month in advance; in December 2023.

Gerald Maurice Clemence was an American astronomer. Inspired by the life and work of Simon Newcomb, his career paralleled the huge advances in astronomy brought about by the advent of the electronic computer. Clemence did much to revive the prestige of the U.S. Nautical Almanac Office.

Jet Propulsion Laboratory Development Ephemeris designates one of a series of mathematical models of the Solar System produced at the Jet Propulsion Laboratory in Pasadena, California, for use in spacecraft navigation and astronomy. The models consist of numeric representations of positions, velocities and accelerations of major Solar System bodies, tabulated at equally spaced intervals of time, covering a specified span of years. Barycentric rectangular coordinates of the Sun, eight major planets and Pluto, and geocentric coordinates of the Moon are tabulated.

Erland Myles Standish Jr. is a mathematical astronomer largely working in the field of solar system dynamics and celestial mechanics. He is a former professor at Yale University and had worked for the Jet Propulsion Laboratory.

A tropical year or solar year is the time that the Sun takes to return to the same position in the sky – as viewed from the Earth or another celestial body of the Solar System – thus completing a full cycle of astronomical seasons. For example, it is the time from vernal equinox to the next vernal equinox, or from summer solstice to the next summer solstice. It is the type of year used by tropical solar calendars.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.