What are ephemerides?
Ephemerides allow the computation of the positions of planets and other bodies at a given time.
People need to calculate the positions of planets and other bodies. The positions of planets are useful for locating them and predicting occultations with other bodies. The positions of the Earth, Sun and Moon are useful for predicting equinoxes, solstices, sunrise, sunset, moonrise, moonset and the time and positions of eclipses.
Traditionally ephemerides were look up tables based on observations. More recent ephemerides consisted of approximations in the form of power series in time which can be computed.
Modern ephemerides are the results of complex numerical integration based on observations. The NASA JPL DE4xx data enables the computation of the positions of the planets, Moon and Sun to a high degree of accuracy. The DE430 data allows positions to be computed for any time between the years 1550 and 2550. These require considerable computing power which modern computers can easily do.
There are also approximations to the DE4xx data which are accurate enough for most purposes. These are suitable for less powerful computers. The VSOP87 data can be used to calculate the positions of the planets, including Pluto. The ELP2000 data can be used to calculate the position of the Moon.