DE400
Encyclopedia
DE400 are designations for the more recent members of a series of astronomical ephemerides
produced by numerical integration at the Jet Propulsion Laboratory
. ('JPL DE' stands for Jet Propulsion Laboratory Development Ephemeris.) The ephemerides of the DE4xx series are expressed in coordinates referred to the ICRF (International Celestial Reference Frame
). These ephemerides provide rectangular (solar-system
barycentric
) coordinates of position and velocity for the Earth-Moon barycenter, Sun
and eight major planet
s, and geocentric
coordinates of the Moon
. These data enable derivation of geocentric or heliocentric
coordinates of relevant bodies. From the issue for 2003 onwards, the Astronomical Almanac
has been based on JPL ephemeris DE405. The DE4xx series of ephemerides is an update to the DE200 ephemeris.
The data have been made publicly available, in the form of data files containing Chebyshev
coefficients, along with source codes for access and basic data-processing to recover positions and velocities, thus amounting to software packages that provide a means of re-generating the positions and velocities of the underlying respective JPL Planetary and Lunar Ephemerides.
Evaluation and interpolation of the Chebyshev polynomial
s can give planetary and lunar coordinates to high precision. DE405 accuracy for the inner planets is about 0.001 arcseconds
(equivalent to about 1 km at the distance of Mars
); for the outer planets it is generally about 0.1 arcseconds. The 'reduced accuracy' DE406 ephemeris gives an interpolating accuracy (relative to the full ephemeris values) no worse than 25 metres for any planet and no worse than 1 metre for the moon.
Documentation for later JPL ephemerides points out the availability of (independently produced) C and Java
interpolating routines.
Nevertheless, the documentation indicates that the ephemerides in this form are not intended for a casual user. They are available for download by anonymous FTP.
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...
produced by numerical integration at the Jet Propulsion Laboratory
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...
. ('JPL DE' stands for Jet Propulsion Laboratory Development Ephemeris.) The ephemerides of the DE4xx series are expressed in coordinates referred to the ICRF (International Celestial Reference Frame
International Celestial Reference Frame
The International Celestial Reference Frame is a quasi-inertial reference frame centered at the barycenter of the Solar System, defined by the measured positions of 212 extragalactic sources . Although relativity implies that there is no true inertial frame, the extragalactic sources used to...
). These ephemerides provide rectangular (solar-system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
barycentric
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
) coordinates of position and velocity for the Earth-Moon barycenter, Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and eight major planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s, and geocentric
Geocentric model
In astronomy, the geocentric model , is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece...
coordinates of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. These data enable derivation of geocentric or heliocentric
Heliocentrism
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...
coordinates of relevant bodies. From the issue for 2003 onwards, 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....
has been based on JPL ephemeris DE405. The DE4xx series of ephemerides is an update to the DE200 ephemeris.
The data have been made publicly available, in the form of data files containing Chebyshev
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...
coefficients, along with source codes for access and basic data-processing to recover positions and velocities, thus amounting to software packages that provide a means of re-generating the positions and velocities of the underlying respective JPL Planetary and Lunar Ephemerides.
Evaluation and interpolation of the Chebyshev polynomial
Polynomial
In mathematics, a polynomial is an expression of finite length constructed from variables and constants, using only the operations of addition, subtraction, multiplication, and non-negative integer exponents...
s can give planetary and lunar coordinates to high precision. DE405 accuracy for the inner planets is about 0.001 arcseconds
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....
(equivalent to about 1 km at the distance of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
); for the outer planets it is generally about 0.1 arcseconds. The 'reduced accuracy' DE406 ephemeris gives an interpolating accuracy (relative to the full ephemeris values) no worse than 25 metres for any planet and no worse than 1 metre for the moon.
Documentation for later JPL ephemerides points out the availability of (independently produced) C and Java
Java (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
interpolating routines.
Nevertheless, the documentation indicates that the ephemerides in this form are not intended for a casual user. They are available for download by anonymous FTP.