The Virtual Observatory
Sky Body Tracker

Version: 3.0 2022-10-01


The SkyBoT (Sky Body Tracker) project has the ambition to provide to astronomers a VO-compliant tool useful to prepare and to analyze astronomical observations of solar system objects. The main usage of SkyBoT services concerns the search for and identification of Solar System objects in astronomical images.

SkyBoT is registered in the IVOA registries under:

  • ID: ivo://vopdc.obspm/imcce/skybot
  • Title: Sky Body Tracker
  • Short Name: SkyBoT

The SkyBoT services can be available through various softwares, in particular:

Implementation of SkyBoT which allows to resolve the name of the solar system objects, and to search for them in any astronomical image (screenshot). You can try it, without any installation process, with the Aladin Java applet. If you have installed Aladin on your computer, you can access to the current release of SkyBoT via the dedicated tab in the server selector. You can also customize your access to SkyBoT by using a special GLU entry. Download the SkyBoT GLU record, save it, adapt it, and restart Aladin with the following argument: aladin -glufile=skybot2.dic.
Implementation of SkyBoT which makes it possible to resolve the name of the solar system objects, to search for them in your own astronomical images, and to point them with your telescope (screenshot). To access the SkytBoT service in Audela, open the "Virtual Observatory" panel.
Implementation of SkyBoT which makes it possible to search for and to identify solar system objects in astronomical images (Menu: Analysis -> Catalogs -> Database -> Skybot).
WCS Tools
Implementation of SkyBoT which makes it possible to search for solar system objects by using a command line program: scat
Implementation of Miriade and SkyBoT in the namespace astroquery.imcce/astroquery.solarsystem.imcce.

Solar system bodies

The Solar System objects recognized by SkyBoT are the planets, their major satellites, the asteroids and the comets. The most direct way to know which objects SkyBoT can search for and identify is to use the SsODNet-Quaero API. For a given object, if the key ephemeris is set to true then positional ephemerides can be computed, and thus SkyBoT will make it appear in the list if it is in the requested field of view. The full list of objects can be retrieved by sending the request ?q=ephemeris:true to the search end-point of the service. Check now.

The following figure and tables show how are classified the population of asteroids and comets, as defined by the international community according to the characteristics of their orbits.

Graphical representation of population classes.
Definition of population classes of asteroids
a = semi-major axis, e = eccentriciy, p = period, R = resonnance x:y, e.g. 5:4, 4:3, 11:8, ...
PopulationSemi-major axis (AU)Aphelion or Perihelion (AU) (*)Comment
Vulcanoid 0.08 ≤ a < 0.21 Yet to be discovered
NEA>Atira 0.21 ≤ a < 1.0 a(1+e) < 0.983 Handful known
NEA>Aten 0.21 ≤ a < 1.0 a(1+e) ≥ 0.983 ~6% of Near Earth Asteroids
NEA>Apollo 1.0 < a < 2.0 a(1-e) < 1.017 ~62% of Near Earth Asteroids
NEA>Amor 1.0 < a < 2.0 1.017 ≤ a(1-e) < 1.3 ~32% of Near Earth Asteroids
Mars-Crosser>Deep 1.0 < a < 2.0 1.3 ≤ a(1-e) ≤ 1.58
Mars-Crosser>Shallow 1.0 < a < 2.0 1.58 ≤ a(1-e) ≤ 1.666
Hungaria 1.0 < a < 2.0 a(1-e) > 1.666
MB>Inner 2.0 ≤ a < 2.5 Inner Main Belt
MB>Middle 2.5 ≤ a < 2.82 Middle Main Belt
MB>Outer 2.82 ≤ a < 3.27 Outer Main Belt
MB>Cybele 3.27 ≤ a < 3.7
MB>Hilda 3.7 ≤ a < 4.6
Trojan 4.6 ≤ a < 5.5 Jupiter Trojans (L4 and L5)
Centaur 5.5 ≤ a < 30.1
KBO>Classical 30.1 ≤ a < 2000.0 Kuiper belt
KBO>Detached 30.1 ≤ a < 2000.0 e ≥ 0.24 Kuiper belt
KBO>SDO 30.1 ≤ a < 2000.0 a(1-e) ≤ 30.1*2^(2/3) * (1-0.24)Kuiper belt
KBO>Classical>Inner 30.1 ≤ a < 39.4 Kuiper belt
KBO>Classical>Main 39.4 ≤ a < 47.8 Kuiper belt
KBO>Classical>Outer 47.8 ≤ a < 2000.0 Kuiper belt
KBO>Resonnant x:y 30.1 ≤ a < 2000.0 a - (30.1*R^(2/3)) ≤ 0.35 Kuiper belt
IOC a ≥ 2000.0 Inner Oort cloud
Definition of population classes of comets
PopulationOrbital Period (year)EccentricityTisserand's invariant
Long-Period P > 200
Short-Period P ≤ 200
Short-Period>Jupiter-family e < 1 TJ > 2
Short-Period>Halley-type e < 1 TJ ≤ 2


The SkyBoT Web service provides the following methods (HTTP + XML + SOAP + WSDL):
SkyBoT Cone-Search
This method allows you to search for and identify all the known solar system objects in a field of view of a given size (circle or box, up to 30°) at a given epoch (see SkyBoT Status method to know the covered period)
SkyBoT Resolver
This method allows you to resolve the names of the solar system objects in their celestial coordinates at a given epoch (see SkyBoT Status method to know the covered period)
And the administrative method:
SkyBoT Status
This method provides the actual status of the database and is useful to know the period of time covered by SkyBoT. Check now!
SkyBoT Availability
This method provides the availability of the SkyBoT web-service. Check now!

Practical use

The SkyBoT cone-search method allows one to retrieve all the known solar system objects located in a time-stamped field of view. This may be useful to identify sources in an astronomical image. The SkyBoT resolver method allows one to quickly compute the ephemeris of any solar system objects at a given date. This may be useful to resolve the designation of a solar system object in celestial coordinates, and to quickly know where it is located on the celestial sphere at a given epoch. However, it is recommended to use the SsODNet API for this.

The SkyBoT service is a SaaS which allows to access methods to search for and identify solar system objects through SOAP requests or by using VO applications such as Aladin or Topcat. The underlying technology (XML+SOAP+WSDL) being inherently interoperable, you can use them and implement them regardless of what your favourite platform and operating system are. For that, you can freely download toolkits client to help you to make the integration of the SkyBoT service seamless with your code.

The easiest way to implement SkyBoT is to use a non-interactive network downloader (e.g. curl, wget) to send HTTP requests and to receive the result "on your desktop". Advanced users may prefer to query SkyBoT directly through its API.

Scientific issues

The SkyBoT service is described in Berthier et al., 2006. The core of SkyBoT is a database of pre-computed ephemeris of all of the known solar system objects (asteroids, planets, natural satellites and comets) over a period which extends from the end of the XIXe century (1889-11-13) to the first half of the XXIe century (2060-03-21). The ephemerides provided by SkyBoT are J2000 astrometric geocentric or topocentric equatorial coordinates (right ascension and declination) at the requested epoch. SkyBoT can also provide J2000 mean heliocentric equatorial rectangular coordinates (position and motion vector) throught the Skbot3D API.

SkyBoT can also provides ephemerides of solar system objects computed for space probes, such as the Rosetta, Kepler, TESS, or the Earth-Sun L2 point. Please contact us if you have a special need that you will like to be implemented in SkyBoT.

The right ascension and declination of the targets are computed by numerical integration of a two bodies problem perturbed by the 8 planets, taking into account relativistic perturbations (post-newtonian approximation). The pre-computed orbits are calculated with the same algorithm, with a sampling step of 1 day and a storage step in the SkyBoT database of 10 days. The dynamical properties of asteroids are issued from the ASTORB database (Lowell Observatory). The dynamical properties of comets are issued from the IMCCE cometary database. The ephemeris of the planets are computed using the INPOP planetary theory. The ephemeris of the natural satellites are computed using various orbital models, depending on the planetary system.

The accuracy of the ephemeris provided by SkyBoT are at the few tens of milli-arcseconds. Depending on the accuracy of asteroid and comet orbits - which depends on the number and the orbital arc spanned by the observations that are fitted - the external accuracy of the ephemeris can be hundreds or thousands of arcseconds in the worst cases. As a consequence, when checking the location of them in astronomical images, it may occur huge errors on the position of some asteroids or comets, especially if they are not accurately known. It will fall within the competence of the user to check and filter the objects before using the data provided by SkyBoT.

Technical issues

SkyBoT is powered by a dedicated hardware infrastructure composed of 10 computing elements. A master/slave system, composed of 1+4 servers, insures the administration, the monitoring and the update of the SkyBoT database. The SkyBoT services run on 4 servers enhanced by a load balancing and failover solution. The servers operate OpenSuse LEAP Linux distribution. The suite of SkyBoT softwares is written in PHP for the services, and Fortran 2013 (using GNU compiler) and MPICH 2 for the parallelized computation of the ephemerides. The data (pre-computed ephemerides) are stored, processed and secured thanks to the MyISAM storage engine of the MariaDB database. The monitoring of the system (hardware and software) is insures by NAGIOS and a home made administration/monitoring interface.

The SkyBoT database is updated weekly to include lately discovered bodies and to update the ephemerides of bodies (mainly asteroids) of which orbits were improved. The hardware infrastructure of SkyBoT allows the service to be available all the time, even when the update process runs. According to the number of asteroids to be updated (few hundreds to a few tens of thousands), you can be brought to wait some time (few hours to two or three days) before being able to access the bodies recently discovered. For comets, the update occurs weekly with the lately discovered objects published by the Minor Planet Center. For planets and natural satellites, the update occurs when new orbital solutions are made available.

The SkyBoT service has been designed and developed by the IMCCE (Observatoire de Paris / CNRS) in the framework of the IMCCE Virtual Observatory project (2004-2010). It is supported by the VO-Paris Data Centre and the french VO. The SkyBoT service is hosted on the IMCCE VO Solar system portal, and is accessible through HTTP query methods and a XML+SOAP+WSDL API.

User support

Each response sent back by the SkyBoT service contains a ticket number. This 18 digits number (e.g. 166134206162181138) identifies each request and may be used to retrieve information on its processing. If you face with errors by using the SkyBoT service (it could occur that no relevant error message is returned), please report us the ticket number corresponding to the problem. It will help you to anderstand and solve it, and you will help us to improve the service.

The information regarding requests sent to SkyBoT is stored in a dedicated database. No personal information is stored, except the IP address provided by the client, which is employed to make statistics on the geographical localization of the SkyBoT users. The SkyBoT logs are never disseminated nor sent on request. You can access to the public logs by using the following URL:[ticket]&method=[method]


Ticket number of the request
Keyword defining the service:
  • Skybot(conesearch), Skybot(resolver),
  • Skybot(status), Skybot(getAvailability)

If you are confronted with a bug, or if you would like to request improvements or special needs, please use the IMCCE Mantis Bug Tracker (Quick access: use the Report issue button in the portal menubar).

Notes to user

The use of the SkyBoT service to search for asteroids in an astronomical archive or in a recent image can present difficulties of interpretation. The main issue may be: is the source in my image the asteroid found by SkyBoT? To answer this question, it may be necessary to pay attention to the following:
  • ensure that the magnitudes are compatible
  • ensure that the ephemeris and the measured position uncertainties are compatible
  • ensure that the accuracy of the epoch is compatible with respect to the target motion

This last point is mandatory because the uncertainty on the epoch can easily shift the computed position of the body by several arcseconds because of its apparent motion on the celestial sphere (from few arcsec per hour to several tens of arcsec per hours for main-belt objects, and more for Near-Earth asteroids). So please, be sure to completely exploit the informations provided by the service (magnitude, error of position, angular velocity, etc).

The error of position of ephemerides provided by SkyBoT gives an estimation of the position uncertainty. This error takes into account only the accuracy of the orbit. The errors which are coming from the computation, the model and the reference frame are not taken into account. For asteroids, this error of position is computed on the basis of the parameters CEU (absolute value of the current 1-σ ephemeris uncertainty) and CEUrate (rate of change of CEU) resulting from ASTORB database.

In any case, the IMCCE cannot be held for person in charge for a misuse or interpretation of the SkyBoT service.

How to cite SkyBoT

If SkyBoT was helpful for your research work, the following acknowledgment would be appreciated: "This research has made use of IMCCE's SkyBoT VO tool", or cite the following article 2006ASPC..351..367B.
\bibitem[Berthier et al.(2006)]{2006ASPC..351..367B} Berthier, J., Vachier, F., Thuillot, W., Fernique, P., 
Ochsenbein, F., Genova, F., Lainey, V., \& Arlot, J.-E.\ 2006, Astronomical Data Analysis Software and 
Systems XV, 351, 367
Bibtex code:
   author = {{Berthier}, J. and {Vachier}, F. and {Thuillot}, W. and {Fernique}, P. and 
             {Ochsenbein}, F. and {Genova}, F. and {Lainey}, V. and {Arlot}, J.-E.},
    title = "{SkyBoT, a new VO service to identify Solar System objects}",
booktitle = {Astronomical Data Analysis Software and Systems XV},
     year = 2006,
   series = {Astronomical Society of the Pacific Conference Series},
   volume = 351,
   editor = {{Gabriel}, C. and {Arviset}, C. and {Ponz}, D. and {Enrique}, S.},
    month = jul,
    pages = {367-+},
   adsurl = {},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}