Editing JPL Horizons On-Line Ephemeris System

{{Short description|Astronomical database}}
{{Use mdy dates|date=January 2025}}
{{primary sources|date=October 2014}}

[[File:JPL Horizons On-Line Ephemeris System output values.png|thumb|Graphic representation of JPL Horizons On-Line Ephemeris System output values<ref>{{Cite web | url=https://www.forumastronautico.it/t/cercansi-collaboratori-per-interfaccia-grafica-nasa-horizons/29002 |title = Cercansi collaboratori per interfaccia grafica NASA Horizons|date = 28 October 2019}}</ref>]]

'''JPL Horizons On-Line Ephemeris System''' provides access to key Solar System data and flexible production of highly accurate [[ephemerides]] for Solar System objects.

[[Osculating orbit|Osculating elements]] at a given [[epoch (astronomy)|epoch]] (such as produced by the [[JPL Small-Body Database]]) are always an approximation to an object's orbit (i.e. an unperturbed conic orbit or a "[[Two-body problem|two-body]]" orbit). The real orbit (or the best approximation to such) considers [[perturbation (astronomy)|perturbations]] by all planets, a few of the [[List of notable asteroids|larger asteroids]], a few other usually small physical forces, and requires [[numerical integration]].

[[Jet Propulsion Laboratory]] (JPL) ephemerides do not use things such as periods, eccentricities, etc.<ref name="jpl-ssd-faq">{{cite web
  |date=2006-02-28
  |title=Frequently Asked Questions (FAQ): What's the exact value of...
  |publisher=[[JPL Solar System Dynamics]]
  |author=Alan B. Chamberlin
  |url=http://ssd.jpl.nasa.gov/?faq#B06
  |access-date=2011-01-20}}</ref> Instead, JPL integrates the [[equations of motion]] in [[Cartesian coordinate system|Cartesian coordinates]] (x,y,z), and adjusts the initial conditions in order to fit modern, highly accurate measurements of planetary positions.<ref name="jpl-ssd-faq"/>

Since August 2013, Horizons has been using [[ephemeris]] [[Jet Propulsion Laboratory Development Ephemeris#Ephemerides in the series|DE431]].<ref>{{Cite web| last = Jet Propulsion Laboratory| title = HORIZONS User Manual| access-date = January 10, 2016| date = August 28, 2015| url = http://ssd.jpl.nasa.gov/?horizons_doc#longterm| at="Long term ephemeridies" section}}</ref> During the week of 12 April 2021, the Horizons ephemeris system was updated to replace the DE430/431 planetary ephemeris, used since 2013, with the new DE440/441 solution. The new DE440/441 general-purpose planetary solution includes seven additional years of ground and space-based astrometric data, data calibrations, and dynamical model improvements, most significantly involving Jupiter, Saturn, Pluto, and the Kuiper Belt. Inclusion of 30 new Kuiper-belt masses, and the Kuiper Belt ring mass, results in a time-varying shift of ~100&nbsp;km in DE441's barycenter relative to DE431.

In September 2021 JPL started transitioning from [[common gateway interface]] (CGI) to [[application programming interface]] (API).

== Ejection ==
Objects (such as [[C/1980 E1]]) on an outbound [[Hyperbolic trajectory|ejection trajectory]] will show an [[Orbital eccentricity|eccentricity]] greater than 1, an [[apoapsis distance]] of AD= 9.99E+99 and an [[orbit period]] of PR= 9.99E+99.<ref name="C1980E1"/> For objects orbiting the Sun, this is best computed at an [[Epoch (astronomy)|epoch]] (date) when the object is outside of the planetary region of the Solar System and no longer subject to notable planetary [[Perturbation (astronomy)|perturbation]]. Due to the [[galactic tide]] and [[List of nearest stars#Distant future and past encounters|passing stars]] it is impossible to know if an object with a weak hyperbolic trajectory will truly be ejected or gently nudged back inward. The galactic tide and passing stars can also cause objects inbound from the Oort cloud to have a weakly hyperbolic trajectory.

== Overview of usage==
There are 3 ways to use the system and all of them can be automated:
* [[WWW|Web]] (partial access)
* [[Email]] (full access)
* [[Telnet]] (full access)
The Horizons system was intended to be easy to use and should have a step-function learning curve.

== References ==
{{Reflist|refs=

<ref name="C1980E1">{{cite web
  | author=Horizons output
  | url=https://ssd.jpl.nasa.gov/horizons_batch.cgi?batch=1&COMMAND=%271980+E1%27&TABLE_TYPE=%27ELEMENTS%27&START_TIME=%271950-01-01%27&STOP_TIME=%272050-01-01%27&STEP_SIZE=%27100%20years%27&CENTER=%27@0%27&OUT_UNITS=%27AU-D%27
  | title=Barycentric Osculating Orbital Elements for Comet C/1980 E1 (Bowell) }} Solution using the Solar System [[Barycenter]]. Ephemeris Type:Elements and Center:@0 (To be outside planetary region, inbound epoch 1950 and outbound epoch 2050)</ref>

}} <!-- end of reflist-->

== External links ==
* [https://ssd.jpl.nasa.gov/horizons/ JPL Horizons On-Line Ephemeris System] ([http://ssd.jpl.nasa.gov/?horizons_doc HORIZONS User Manual])
* [https://ssd.jpl.nasa.gov/horizons_batch.cgi HORIZONS Batch-Interface CGI] / [https://ssd-api.jpl.nasa.gov/ JPL SSD/CNEOS API]

[[Category:Astrometry]]
[[Category:Astronomy websites]]
[[Category:JPL online services]]