Jet Propulsion Laboratory Developmental Ephemeris
Encyclopedia
The name Jet Propulsion Laboratory Development Ephemeris (followed by a number), or its abbreviation JPL DE (+ number), designates one of a series of numbered versions of the astronomical ephemerides produced at the Jet Propulsion Laboratory
in Pasadena, California
, primarily for purposes of space navigation and astronomy. Some versions of these ephemerides are or have been in official use: for example, the Astronomical Almanac
issues for 1984 onwards through 2002 were based on JPL ephemeris DE200, and for 2003 onwards the Astronomical Almanac has been based on JPL ephemeris DE405.
Each such ephemeris
was initially produced by numerical integration of equations of motion, including the effects not only of gravitational accelerations and relativistic corrections, but also tidal and figure effects and a model of the lunar librations. The time argument of the integrated ephemerides is a relativistic coordinate time scale designated Teph.
The resulting ephemeris data are stored or distributed in the form of a system of numerical coefficients (for Chebyshev polynomials
) which can be used to recover (calculate) the positions of the major planets of the solar system (with the Moon and Pluto, and in some cases also with data for the lunar librations and/or earth-axis nutations) for a range of dates, usually both in the past and the future, according to the interval of the original numerical integration.
The positions given by the calculations represent the development, by integration of the chosen equations of motion, of a "best fit" set of initial conditions adjusted to a (large) selected set of observations. The observational data included in the fits by which each ephemeris is produced has been an evolving set, usually including: ranges (distances) to planets measured by radio signals from spacecraft, astronomical observations of planets and small bodies in the solar system, and data derived from lunar laser-ranging, among others.
There are many different versions of the JPL DE, each one with a 2- or 3-digit serial number following. They differ according to the year the data was revised and released, and according to the accuracy and time-range that each JPL DE covers.
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
in Pasadena, California
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...
, primarily for purposes of space navigation and astronomy. Some versions of these ephemerides are or have been in official use: for example, the Astronomical Almanac
Astronomical Almanac
The Astronomical Almanac is an almanac published by the United States Naval Observatory and Her Majesty's Nautical Almanac Office, containing solar system ephemeris and catalogs of selected stellar and extragalactic objects....
issues for 1984 onwards through 2002 were based on JPL ephemeris DE200, and for 2003 onwards the Astronomical Almanac has been based on JPL ephemeris DE405.
Each such ephemeris
Ephemeris
An ephemeris is a table of values that gives the positions of astronomical objects in the sky at a given time or times. Different kinds of ephemerides are used for astronomy and astrology...
was initially produced by numerical integration of equations of motion, including the effects not only of gravitational accelerations and relativistic corrections, but also tidal and figure effects and a model of the lunar librations. The time argument of the integrated ephemerides is a relativistic coordinate time scale designated Teph.
The resulting ephemeris data are stored or distributed in the form of a system of numerical coefficients (for Chebyshev polynomials
Chebyshev polynomials
In mathematics the Chebyshev polynomials, named after Pafnuty Chebyshev, are a sequence of orthogonal polynomials which are related to de Moivre's formula and which can be defined recursively. One usually distinguishes between Chebyshev polynomials of the first kind which are denoted Tn and...
) which can be used to recover (calculate) the positions of the major planets of the solar system (with the Moon and Pluto, and in some cases also with data for the lunar librations and/or earth-axis nutations) for a range of dates, usually both in the past and the future, according to the interval of the original numerical integration.
The positions given by the calculations represent the development, by integration of the chosen equations of motion, of a "best fit" set of initial conditions adjusted to a (large) selected set of observations. The observational data included in the fits by which each ephemeris is produced has been an evolving set, usually including: ranges (distances) to planets measured by radio signals from spacecraft, astronomical observations of planets and small bodies in the solar system, and data derived from lunar laser-ranging, among others.
There are many different versions of the JPL DE, each one with a 2- or 3-digit serial number following. They differ according to the year the data was revised and released, and according to the accuracy and time-range that each JPL DE covers.
Sources
- X X Newhall, E M Standish, & J G Williams (1983), "DE 102 - A numerically integrated ephemeris of the moon and planets spanning forty-four centuries", Astronomy and Astrophysics (ISSN 0004-6361), vol.125, no.1, Aug.1983, pp.150-167.
- .
- E M Standish (1998), [ftp://ssd.jpl.nasa.gov/pub/eph/planets/ioms/de405.iom.pdf JPL Planetary and Lunar Ephemerides, DE405/LE405], Jet Propulsion Laboratory Interoffice Memorandum 312F-98-48, August 26, 1998.
External links
- [ftp://ssd.jpl.nasa.gov/pub/eph/planets/ JPL FTP site] with ephemerides (data files), source code (for access and basic processing of the data to recover positions and velocities), and documentation.
- [ftp://ssd.jpl.nasa.gov/pub/eph/planets/ioms/ JPL Interoffice Memoranda] describing features of the ephemerides.
- US Naval Observatory (Naval Oceanography Portal), "History of the Astronomical Almanac" (accessed December 2009).