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Credits

Plate solving

Sideris identifies the region of sky in a photograph using a modified version of the Astrometry.net plate-solving engine, compiled as a native library and bundled with the application so that solving requires no network connection and no account.

The engine, and the blind-calibration method behind it, are the work of the Astrometry.net team. The reference publication is: D. Lang, D. W. Hogg, K. Mierle, M. Blanton and S. Roweis, "Astrometry.net: Blind astrometric calibration of arbitrary astronomical images", The Astronomical Journal, volume 139, pages 1782 to 1800 (2010).

The version bundled here has been modified to remove components the application does not use and to replace two of its dependencies. The inherited code remains under the 3-clause BSD license, the full text of which is reproduced under Open Source Licenses, together with the University of California's notice for a sorting routine the library takes from FreeBSD.

The Astrometry.net team is not affiliated with Sideris and does not endorse it. Their name appears here to identify the origin of the software, as the license requires, and for no other purpose.

Star catalogue

The star positions drawn on the sky map, and the index files the solver searches, derive from Astrometry.net's index series 4100, which is built from the Tycho-2 catalogue: E. Hoeg, C. Fabricius, V. V. Makarov and others, "The Tycho-2 Catalogue of the 2.5 million brightest stars", Astronomy & Astrophysics, volume 355, pages L27 to L31 (2000).

Constellation figures

The constellation lines drawn on the sky map are the stick figures published by the International Astronomical Union in collaboration with Sky & Telescope magazine (Alan MacRobert, Roger Sinnott and Rick Fienberg), which are made available under the Creative Commons Attribution 4.0 International License. They are taken from the machine-readable transcription by Dominic Ford (In-The-Sky.org). The figures' star identifiers have been resolved to coordinates against the Hipparcos catalogue and re-encoded for size; the figures themselves have not been altered.

Deep Sky Objects Catalog

The galaxies, nebulae and star clusters that Sideris lists and draws on the sky map come from a catalogue compiled for the application from the sources below, merged so that each object appears once under all of its designations.

The objects of the New General Catalogue and the Index Catalogue are taken from OpenNGC by Mattia Verga (https://github.com/mattiaverga/OpenNGC), which is made available under the Creative Commons Attribution-ShareAlike 4.0 International License (https://creativecommons.org/licenses/by-sa/4.0/). OpenNGC is compiled from the NASA/IPAC Extragalactic Database, HyperLEDA, SIMBAD, HEASARC and the work of Harold G. Corwin. The catalogue bundled with Sideris is an adaptation of OpenNGC: it has been filtered, merged with the catalogues listed below and re-encoded. It is distributed under the same license, and a copy can be downloaded from https://siderisstudio.com/data/sideris-dso.tsv.

The other catalogues were obtained through the VizieR catalogue access tool of the Centre de Données astronomiques de Strasbourg, CDS, Strasbourg, France (DOI 10.26093/cds/vizier). Their authors are: S. Sharpless, "A Catalogue of H II Regions", Astrophysical Journal Supplement Series, volume 4, page 257 (1959); B. T. Lynds, "Catalogue of Bright Nebulae", Astrophysical Journal Supplement Series, volume 12, page 163 (1965); B. T. Lynds, "Catalogue of Dark Nebulae", Astrophysical Journal Supplement Series, volume 7, page 1 (1962); E. E. Barnard, "A Photographic Atlas of Selected Regions of the Milky Way", Carnegie Institution of Washington (1927); S. van den Bergh, "A study of reflection nebulae", Astronomical Journal, volume 71, page 990 (1966); A. W. Rodgers, C. T. Campbell and J. B. Whiteoak, "A catalogue of H-alpha emission regions in the southern Milky Way", Monthly Notices of the Royal Astronomical Society, volume 121, page 103 (1960); B. Cederblad, "Studies of bright diffuse galactic nebulae", Meddelanden från Lunds Astronomiska Observatorium, Series II, number 119 (1946); H. Arp, "Atlas of Peculiar Galaxies" (1966), in the index prepared by D. Webb (1996); P. Hickson, "Systematic properties of compact groups of galaxies", Astrophysical Journal, volume 255, page 382 (1982); G. O. Abell, H. G. Corwin and R. P. Olowin, "A catalog of rich clusters of galaxies", Astrophysical Journal Supplement Series, volume 70, page 1 (1989); A. Acker, F. Ochsenbein, B. Stenholm, R. Tylenda, J. Marcout and C. Schohn, "Strasbourg-ESO Catalogue of Galactic Planetary Nebulae", European Southern Observatory (1992); D. A. Green, "A Catalogue of Galactic Supernova Remnants", October 2024 version, Cavendish Laboratory, Cambridge; and N. V. Kharchenko, A. E. Piskunov, E. Schilbach, S. Röser and R.-D. Scholz, "Global survey of star clusters in the Milky Way II", Astronomy and Astrophysics, volume 558, A53 (2013), for the Collinder, Melotte, Trumpler, Stock, Ruprecht and van den Bergh-Hagen clusters.

The Messier objects keep the names, sizes and distances the application has always shown. The Herschel 400 list is that of the Astronomical League. Constellations are assigned with the boundaries published by N. G. Roman, Publications of the Astronomical Society of the Pacific, volume 99, page 695 (1987).

The common names of the objects were each confirmed against an independent source, chiefly Wikipedia and the SIMBAD database, operated at CDS, Strasbourg, France, before being included.

Astronomical calculations

The positions of the Sun, the Moon, the planets, the phases shown in the moon calendar, the precession and sidereal time used by the polar scope, and the sun altitude that drives automatic night mode are all computed on the device from the algorithms published in Jean Meeus, "Astronomical Algorithms", second edition (Willmann-Bell, 1998).

The implementations are original to Sideris. No source code from the book or from any software accompanying it is included in the application.

Magnetic declination

When the sky map follows the device's motion sensors, the compass heading those sensors report is turned from magnetic north to true north using the magnetic declination at the observing location. The declination is computed on the device from the World Magnetic Model 2025, produced by the National Centers for Environmental Information of the United States National Oceanic and Atmospheric Administration and the British Geological Survey: NOAA NCEI Geomagnetic Modeling Team and British Geological Survey, "World Magnetic Model 2025", NOAA National Centers for Environmental Information (2024), https://doi.org/10.25921/aqfd-sd83. The model's coefficients are included unaltered. They are material of the United States Government, in the public domain and not subject to copyright protection. The implementation is original to Sideris.

Map data

The offline map used to set an observing location by hand is drawn from two public datasets, both bundled with the application so that the map requires no network connection.

The coastlines, international boundaries, first-level administrative boundaries, lakes, rivers, roads, and the names of countries, administrative divisions and towns are derived from Natural Earth, which places its data in the public domain. Natural Earth is supported by the North American Cartographic Information Society.

The list of populated places, and the country names shown beside them, are derived from the GeoNames geographical database, which is made available under the Creative Commons Attribution 4.0 International License. The data has been reduced and re-encoded for size; it has not been otherwise altered.

Typography

Sideris uses two typefaces, both bundled with the application and both licensed under the SIL Open Font License, Version 1.1.

The full text of the SIL Open Font License is distributed with the application alongside the font files.

Astronomical imagery

The deep-sky object images shown in Sideris are in the public domain, having been created by NASA and ESA. NASA Hubble material (and ESA Hubble material prior to 2009) is copyright-free and may be freely used in the public domain without fee, on the condition that only NASA, STScI, and/or ESA is credited as the source of the material.

This material was created for NASA by the Space Telescope Science Institute under Contract NAS5-26555, or for ESA by the Hubble European Space Agency Information Centre.

Source: NASA, STScI, and ESA, via Wikimedia Commons.