Your Sky: Credits


Your Sky was implemented by John Walker in January and February of 1998. The calculation and display software was adapted from Home Planet for Windows.

The GIF output file generation is based upon the ppmtogif module of Jef Poskanzer's pbmplus toolkit, of which many other components were used in creating the images you see here.

   ppmtogif.c - read a portable pixmap and produce a GIF file
  
   Based on GIFENCOD by David Rowley [mgardi@watdscu.waterloo.edu].
   Lempel-Zim compression based on "compress".
  
   Modified by Marcel Wijkstra [wijkstra@fwi.uva.nl]
  
   Copyright © 1989 by Jef Poskanzer.
  
   Permission to use, copy, modify, and distribute this software and its
   documentation for any purpose and without fee is hereby granted, provided
   that the above copyright notice appear in all copies and that both that
   copyright notice and this permission notice appear in supporting
   documentation.  This software is provided "as is" without express or
   implied warranty.
  
   The Graphics Interchange Format© is the Copyright property of
   CompuServe Incorporated.  GIF(sm) is a Service Mark property of
   CompuServe Incorporated.

Steven Grimm's uncgi made the task of processing form arguments in the server immeasurably easier.

The algorithms to calculate the positions of the Moon, planets, asteroids, and comets are given in:

Meeus, Jean. Astronomical Algorithms . Richmond: Willmann-Bell, 1998. ISBN 0-943396-63-8.

Stars in full-sky maps and horizon views are plotted using “The Bright Star Catalogue, 5th Revised Edition” [Yale: Hoffleit & Warren 1991], which contains position, magnitude, spectral type, and proper motion data for 9096 stars brighter than magnitude 6.5. It is the most widely used digital star database, since it includes comprehensive information for all naked eye stars. The master versions of this catalogue is distributed on the NASA Astronomical Data Center CD-ROM, were specially processed for use in Your Sky, annotating them with star names, Bayer letters and Flamsteed numbers, and other information. You can obtain copies of this and other astronomical catalogues from the Astronomical Data Center's Archives.

The Virtual Telescope uses the definitive Smithsonian Astrophysical Observatory Star Catalogue [SAO: 1966], updated to epoch J2000.0 and corrected by Roman and Warren in 1990. The SAO catalogue is the fundamental professional astrometric reference: it lists more than a quarter of a million stars, providing position, visual and photographic magnitude, proper motion, spectrographic information, and a wealth of other data. The SAO catalogue contains stars as faint as twelfth magnitude, but is generally considered to have a limiting magnitude (the point at which as many stars are missed as are included) of about 9.5. The master versions of these primary references, distributed on the Astronomical Data Center CD-ROM, were specially processed for use in Your Sky, annotating them with star names, Bayer letters and Flamsteed numbers, and other information. Visit the Astronomical Data Center's Archives for your own copy of this database.

The images used in the Your Sky welcome page and the help logo were synthesised using the “noao/artdata” artificial star field generator module of the National Optical Astronomy Observatories' IRAF system. IRAF is an extremely powerful professional image analysis and processing program, and it's free. To generate your own custom star fields and planets, check out our Terranova Screen Saver for Windows. The shadow was added using the Fourmilab Shadow Server.

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