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Sources of calculations and data

This page gathers the external sources on which the calculations and the images of WinStars 3 rely, with the references needed to consult and check them. It also helps locate the origin of a local disagreement between the position shown by the program and that of a recent catalogue.

Star catalogue: Gaia

The WinStars 3 star catalogue is based on Gaia EDR3 (Early Data Release 3), published by ESA on 15 December 2020. It contains 1,811,704,130 sources, with positions, parallaxes, proper motions and photometry (G, GBP, GRP bands). The G magnitude of the faintest sources is about 21.

  • Scientific reference: Gaia Early Data Release 3 — A. G. A. Brown et al., 2021, Astronomy & Astrophysics 650, A1; abstract on arXiv: arXiv:2012.01533.

  • Online database: ESA Gaia archive.

  • Angular precision: about 0.02 to 0.03 milliarcsecond (mas) for the brightest stars, and about 0.5 mas near magnitude G = 20. One milliarcsecond is 1/1000 of an arcsecond, that is 1/3,600,000 of a degree.

The Gaia DR3 catalogue (13 June 2022, arXiv:2208.00211) extends EDR3: it provides about 333 million complete six-parameter astrometric solutions, radial velocities, classified spectra and light curves. WinStars 3 uses the EDR3 version. The division of the catalogue into three parts inside the software, and the on-demand download rules, are described on the Star catalogues page.

Planets and Moon: numerical ephemerides from JPL

Planetary positions are computed with the DE438 numerical ephemeris of the Jet Propulsion Laboratory (JPL, NASA), not with an approximate analytical theory. In its official publication the de438.bsp kernel covers the period from 31 December 1549 to 25 January 2650: it provides the positions of the barycentres of the planets from Mercury to Pluto, of the Sun, of the Moon and of the Earth, with respect to the solar system barycentre.

  • File and period published by NASA in the SPICE system (NAIF): planetary SPK kernel directory, and its technical summary aa_summaries.txt, which states the exact period covered by each kernel.

  • The software uses this kernel for the planets, for the Moon and for Pluto: eclipses, occultations and the height of the Moon rest on the same numerical solution as the positions of the planets.

  • A numerical ephemeris is a solution of the solar system obtained by integration: very accurate inside the published period, it does not extend mathematically outside it. Beyond the published period the software extrapolates the kernel: the position shown is still computed, but it is no longer constrained by NASA’s integrated solution. The Technical factsheet page states the same limit.

Deep sky

  • OpenNGC: open catalogue of clusters, nebulae and galaxies, an extension of the NGC and IC catalogues: openngc.queryfactory.org.

  • EDD (the Eso-Lund catalogue of nearby galaxies and its extensions): nearby galaxies, used for the three-dimensional representation: see 3D navigation mode.

  • PGC (Principal Galaxy Catalog): close to 74,000 galaxies designated PGC, the working database of many galaxy catalogues.

Solar system objects

  • Minor Planet Center (MPC), an International Astronomical Union service: it collects observations and publishes the orbits of asteroids and comets. The lists loaded by WinStars come from its public files: minorplanetcenter.net/_NETWORK_INFO/. The MPC records more than 1.3 million observed objects, of which about 640,000 are numbered, and a little more than 400 numbered periodic comets.

  • Orbital parameters age: that is why the Asteroides and Cometes dialog boxes offer to refresh them from the server. An object discovered after the last update of your software may be missing from the lists.

Artificial satellites

  • The orbital elements (TLE) come from the public trajectory distributors, for instance CelesTrak or Space-Track.

  • Propagation in time uses the SGP4 and SDP85 models. These models approximate the trajectory: precision degrades quickly with the age of the element, which explains why the TLE must be reloaded before a serious observation. See Satellites.

Exoplanets

  • The list of confirmed worlds follows the NASA Exoplanet Archive, which publishes the official count (about 6,000 confirmed planets). The exact number shown by WinStars depends on the installed module.

Sky atlas: DSS

  • The Digitized Sky Survey is an electronic version of photographic atlases, distributed by the Space Telescope Science Institute: see DSS function.

  • Reference points: the Palomar Observatory Sky Survey (POSS) plates have a limiting magnitude of about 20.3, and the DSS is sampled at about 1.69 arcseconds per pixel. The DSS is a plate survey: variable objects, moving small bodies and very compact objects may appear badly there, or not at all.

Time and Earth rotation

  • ΔT is the cumulative difference between Terrestrial Time (TT) and Universal Time (UT): ΔT = TT − UT. A one-second difference shifts equatorial coordinates by about 15 seconds of right ascension.

  • Models used by the menu: see Time and date setting.

  • Reference of the polynomials proposed by the software: Five Millennium Canon of Solar Eclipses (F. Espenak & J. Meeus, 2006), NASA — valid from −1900 to +2200.

  • Most recent scientific reference commonly quoted: A long-term daily model of the Earth’s variable rotational motion (R. G. A. Stephenson, F. R. Stephenson, L. J. Morrison & C. V. Hohenkerk, 2016), Proceedings of the Royal Society A — valid from −1800 to +2200.

  • Measured values and official predictions: IERS Earth Orientation Service (Bulletins A and B).

Instruments

Updating the data

None of these sources is frozen: published catalogues and orbits keep changing. The Modules, Asteroides, Cometes and Satellites dialog boxes and the Maintenance feature (clearing the cache) are the means provided to catch up.