Editing Ephemeris (section)

== Modern ephemeris ==
For scientific uses, a modern planetary ephemeris comprises software that generates positions of planets and often of their satellites, [[asteroid]]s, or [[comet]]s, at virtually any time desired by the user.

After introduction of electronic computers in the 1950s it became feasible to use [[numerical integration]] to compute ephemerides. The [[Jet Propulsion Laboratory Development Ephemeris]] is a prime example. Conventional so-called analytical ephemerides that utilize series expansions for the coordinates have also been developed, but of much increased size and accuracy as compared to the past, by making use of computers to manage the tens of thousands of terms. [[Ephemeride Lunaire Parisienne]] and [[VSOP (planets)|VSOP]] are examples.

Typically, such ephemerides cover several centuries, past and future; the future ones can be covered because the field of [[celestial mechanics]] has developed several accurate theories. Nevertheless, there are [[Secular variation|secular phenomena]] which cannot adequately be considered by ephemerides. The greatest uncertainties in the positions of planets are caused by the perturbations of numerous [[asteroid]]s, most of whose masses and orbits are poorly known, rendering their effect uncertain. Reflecting the continuing influx of new data and observations, [[NASA]]'s Jet Propulsion Laboratory ([[JPL]]) has revised its [[Jet Propulsion Laboratory Development Ephemeris|published ephemerides]] nearly every year since 1981.<ref>[[Georgij A. Krasinsky]] and [[Victor A. Brumberg]], ''Secular Increase of Astronomical Unit from Analysis of the Major Planet Motions, and its Interpretation'' [https://link.springer.com/article/10.1007/s10569-004-0633-z Celestial Mechanics and Dynamical Astronomy 90: 267–288, (2004)].</ref>

[[Solar System]] ephemerides are essential for the navigation of [[spacecraft]] and for all kinds of space observations of the [[planet]]s, their [[natural satellite]]s, [[star]]s, and [[Galaxy|galaxies]].

Scientific ephemerides for sky observers mostly contain the positions of celestial bodies in [[right ascension]] and [[declination]], because these coordinates are the most frequently used on star maps and telescopes. The [[Equinox (celestial coordinates)|equinox]] of the coordinate system must be given. It is, in nearly all cases, either the actual equinox (the equinox valid for that moment, often referred to as "of date" or "current"), or that of one of the "standard" equinoxes, typically [[J2000.0]], [[B1950.0]], or J1900. Star maps almost always use one of the standard equinoxes.

Scientific ephemerides often contain further useful data about the moon, planet, asteroid, or comet beyond the pure coordinates in the sky, such as elongation to the Sun, brightness, distance, velocity, apparent diameter in the sky, phase angle, times of rise, transit, and set, etc.
Ephemerides of the planet [[Saturn]] also sometimes contain the apparent inclination of its ring.

[[Celestial navigation]] serves as a backup to [[satellite navigation]]. Software is widely available to assist with this form of navigation; some of this software has a self-contained ephemeris.<ref>{{cite book | title = American Practical Navigator: An Epitiome of Navigation | date = 2002 | page = 270 | publisher = National Imagery and Mapping Agency | location = Bethesda, MD | url = http://msi.nga.mil/NGAPortal/MSI.portal?_nfpb=true&_pageLabel=msi_portal_page_62&pubCode=0002}}</ref> When software is used that does not contain an ephemeris, or if no software is used, position data for celestial objects may be obtained from the modern ''[[Nautical Almanac]]'' or ''Air Almanac''.<ref>{{Cite web| title = Almanacs and Other Publications — Naval Oceanography Portal| access-date = 11 November 2016| url = http://www.usno.navy.mil/USNO/astronomical-applications/publications| publisher = [[United States Naval Observatory]]| archive-date = 27 January 2022| archive-url = https://web.archive.org/web/20220127194119/https://www.usno.navy.mil/USNO/astronomical-applications/publications| url-status = dead}}</ref>

An ephemeris is usually only correct for a particular location on the Earth. In many cases, the differences are too small to matter. However, for nearby [[asteroid]]s or the [[Moon]], they can be quite important.

Other modern ephemerides recently created are the EPM (Ephemerides of Planets and the Moon), from the Russian Institute for Applied Astronomy of the [[Russian Academy of Sciences]],<ref>{{cite journal|last=Pitjeva|first=Elena V.|title=The dynamical model of the planet motions and EPM ephemerides|journal=Highlights of Astronomy|date=August 2006|volume=2|issue=14|pages=470|doi=10.1017/S1743921307011453|bibcode=2007HiA....14..470P|doi-access=free}}</ref> and the INPOP (''{{lang|fr|Intégrateur numérique planétaire de l'[[Observatoire de Paris]]}}'') by the French [[IMCCE]].<ref>{{cite web|title=INPOP10e, a 4-D planetary ephemeris|url=http://www.imcce.fr/inpop/|publisher=IMCCE|access-date=2 May 2013}}</ref><ref>{{cite journal |last1=Viswanathan |first1=V. |last2=Fienga |first2=A. |last3=Gastineau |first3=M. |last4=Laskar |first4=J. |title=INPOP17a planetary ephemerides |journal=Notes Scientifiques et Techniques de l'Institut de Mécanique Céleste |date=1 August 2017 |volume=108 |pages=108 |doi=10.13140/RG.2.2.24384.43521 |bibcode=2017NSTIM.108.....V }}</ref>