Ephemeris

In the study of celestial bodies, an ephemeris , ephemeris or ephemeris (plural: anniversaries , the Greek á¼uήμεuοu, ephemera , "day") is a table of values that gives the positions of astronomical objects in the sky at a time or times dice. Different types are used in astronomy and astrology . Although it was also one of the first applications of mechanical computers, the term ephemeris generally continues to apply a simple printed table. The position is represented in the form of spherical polar coordinates for astronomers, and length along the ecliptic zodiac , and sometimes decline to astrologers. The positions of the planets can be both for the noon to the midnight . An ephemeris astronomical phenomena provides data on astronomical interest to astronomers and astrologers, such as eclipses , stations retrograde movements / planetary, planetary disappearance prior to an eclipse, sidereal time , positions of the nodes Real y Medio, the phases of Moon , and sometimes even the position or positions of Chiron , and other celestial bodies minors. Astrologers also use other ephemera including imaginary celestial tables, such as Lilith , a term used variously to the height of the Moon or the second focus of the lunar orbit. Some ephemerides also contain a Aspectarian monthly, while others generally include the decline of the planets and their longitudes, right ascensions or Cartesian coordinates .

It is said that Christopher Columbus , being a castaway on the island of Jamaica, predicted in 1504 successfully a lunar eclipse for the natives of that island, using the ephemeris of the German astronomer Regiomontanus . Among other things, also known to Johannes Stadius published in 1554 a well-known book called Ephemerides novae at auctae in which she intended to give accurate planetary positions. His effort was not entirely satisfactory, and there was, for example, periodic errors in the positions predicted by the planet Mercury Stadius up to ten degrees.

Scientific Ephemeris

A modern planetary ephemeris is a software that generates positions of the planets and their satellites generally, or asteroids or comets at virtually any time desired by the user. Often there is an option to find the velocities of the bodies of interest, too.

Normally, such ephemerides cover several centuries, past and future, the future can be covered because celestial mechanics is an accurate theory. However, there are secular phenomena , factors that can not be properly considered by the ephemeris. The major uncertainties on the planetary positions are due to perturbations of many asteroids, most of whose masses are poorly known, leading to an uncertain outcome. Therefore, despite efforts to avoid these uncertainties, the JPL have to revise its published ephemerides at intervals of 20 years.

The ephemeris of the solar system are essential for navigating the spacecraft and all kinds of space observations of the planets, their moons , the stars and galaxies .

Scientific ephemerides for sky observers mostly contain the position of said celestial body in right ascension and declination , as these coordinates are the most frequently used star maps and telescopes. Be provided the equinox of the coordinate system. In almost all cases is the actual equinox (the valid time), or one of the standard equinoxes, typically J2000.0 , B1950.0 , or J1900. Star maps are almost always in one of the standard equinoxes.

The scientific ephemeris often contain additional useful data on the moon, planet, asteroid or comet beyond the pure coordinates in the sky, such as the elongation , brightness, distance, velocity, apparent diameter, phase angle, time of departure transit or entry.

The ephemeris of the planet Satu also contain the apparent tilt of its rings.

An accurate ephemeris is usually only for a particular place on Earth. In many cases the differences are too small to matter, but for nearby asteroids or the Moon can be quite substantial.

Satellite navigatio GPS ephemeris transmit electronic information consisting of elevation and exact location data that GPS receivers use later (along with the time taken for the signal to reach the receiver) to calculate its own location on Earth using trilateration .

Astrological Ephemeris

Most astrologers studied tropical astrology , which involves the planetary positions regarding the position of the equinox vernal (spring) along the ecliptic (the equinox being the link betwee Earth's rotational plane and the plane around the Sun) . Use exactly the same frame of reference for astronomers, except for a small minority of astrologers who study sidereal astrology and use a different ephemeris, based on the constellations.

Although astrology is and always has been geocentric , astrology heliocentric is an emerging field, for this purpose can not use a standard ephemeris, and because of this should be calculated and used specialized heliocentric ephemeris instead of geocentric ephemerides used in Western astrology to build the chart .