\b0 while probing the Internet archives for games with my son. I've had a lot of fun with it, tracking the planets across the sky. It is freely distributed for Microsoft Windows, and I thought it would be nice to have a NEXTSTEP version as well. The author, Stephen Michael Schimpf, was kind enough to supply me with the source for this purpose. The interface is based on the original Windows interface, but was completely rewritten for the NEXTSTEP environment. The original code for the astronomical algorithms was neatly modularized, and I was able to use it without modification.\
The original
\b SkyView
\b0 was developed by Stephen Michael Schimpf about five years ago when he was still an undergraduate working for Drs. Plavec and Keyes at the UCLA Department of Astronomy. This original program was written entirely in FORTRAN and ran on a VAX 750. The sky display was produced on a Ramtek monitor and projected in a classroom. Professors displayed the sky for hundreds of students taking introductory astronomy classes each quarter at UCLA.\
\li0 \
\li180 After starting the FORTRAN version he developed a DOS version of
\b SkyView
\b0 for his own use at home. He targeted the program not at education but for use by amateur astronomers who wanted to plan their telescope time in advance. Later he developed a version for Windows 3.0, which was distributed to friends. Finally, he wrote the necessary documentation and packaged
\b SkyView
\b0 so it could be distributed freely. \
\b Contacting the Authors
\b0 \
If you have any questions, comments, or suggestions for improvements, we can be contacted by USPS or Internet mail using the following addresses:\
\pard\tx520\tx1060\tx1600\tx2120\tx2660\tx3200\tx3720\tx4260\tx4800\tx5320\f0\b\i\ulnone\fs28\fc1\cf1 Introduction to SkyView 1.0\
\b0\i0\fs24\gray300\fc2\cf2 \
\b\li180\gray0\fc0\cf0 SkyView
\b0 performs many of the functions of a planetarium. It allows you to see the appearance of the sky from any specified location on the earth. You can change the date and time for which the sky is displayed to see the sky as it looked in the past or as it will look in the future.\
\b SkyView
\b0 displays the positions of the sun, moon, and all naked-eye planets, as well as all the stars down to a limiting magnitude you select. You can orient the sky display so that the North, South, East, or West horizon is positioned at the bottom of the screen. The ecliptic, celestial equator, galactic equator, and equatorial coordinate lines can be added to the display in any combination. You even have control of the colors used for most of the sky objects and for the background.\
\b Definitions
\b0 \
\b\gray246\fc3\cf3 ecliptic
\b0\gray0\fc0\cf0 is the great circle which the plane of the earth's orbit around the sun forms where it intersects the celestial sphere. In simpler words, the ecliptic is the line in the sky along which the sun appears to move during the course of a year. The sun moves roughly one degree along this line every day. Because the orbits of the naked-eye planets have inclinations of seven degrees or less, you will always find the planets on or very close to this line.\
\b\gray246\fc4\cf4 celestial equator
\b0\gray0\fc0\cf0 is simply the great circle formed by extending the earth's equatorial plane out to the celestial sphere. The axis of the earth's daily rotation is tilted with respect to its orbital plane, and therefore the ecliptic and celestial equator are tilted with respect to each other. This angle, known as the obliquity of the ecliptic, is currently roughly 23.5 degrees.\
\b\gray246\fc5\cf5 galactic equator
\b0\gray0\fc0\cf0 is the equator of our galaxy, the Milky Way. You will notice that at large limiting magnitudes the number of stars in the sky display is larger around the galactic equator than in other areas of the sky. You are seeing the concentration of stars along the plane of our galaxy.\
Lines of the equatorial coordinate system are displayed ten degrees apart. The lines that run from pole to pole are lines of
\b\gray246\fc5\cf5 right ascension
\b0\gray0\fc0\cf0 , and those that run parallel to the celestial equator are lines of
\b\gray246\fc5\cf5 declination
\b0\gray0\fc0\cf0 . The right ascension and declination system is similar to the longitude and latitude system used on the surface of the earth.\
\b\gray246\fc5\cf5 Magnitudes
\b0\gray0\fc0\cf0 are used in astronomy for historical reasons. In ancient times the stars were ranked in six classes of magnitude. The brightest stars were first magnitude and the faintest just visible to the naked eye were sixth magnitude. This system became inadequate with the invention of the telescope, when many fainter stars were discovered.\
In 1856 the English astronomer N.R. Pogson proposed that a difference of five magnitudes correspond exactly to a brightness ratio of 100 to 1. The brightness ratio of two stars that differ by one magnitude is the fifth-root of 100, or 2.512, a quantity known as the Pogson ratio. A star that has a magnitude two less than another star is 2.512 squared, or about 6.3 times brighter than the other star. \
The larger the limiting magnitude you select the more faint stars will be displayed. Selecting 6.4 as a limiting magnitude will display all 7788 stars in the
\b SkyView
\b0 database. You only see half this many stars at one time because you only see half of the sky at one time. Also, you will only be able to see down to magnitude 6 under very good seeing conditions far away from city lights.\
For more information about the astronomical calculations performed in
\b SkyView
\b0 , see:\
\li0 \
\li720 Duffett-Smith, P. 1990, Astronomy with Your Personal Computer, \
Second Edition, (Cambridge: Cambridge University Press). \
ISBN 0-521-38995-X.\
Green, R.M. 1985, Spherical Astronomy, \
(Cambridge: Cambridge University Press).\
Meeus, J. 1991, Astronomical Algorithms. \
(Richmond: Willmann-Bell). ISBN 0-943396-35-2.\
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lCopyright 1993, Corona Design, Inc. All Rights Reserved.
\b0\i0\fs24\li180\fc0\cf0 This program is provided "as-is". In no event shall Corona Design, Inc. or Steven Michael Schimpf (collectively the "Authors") be liable for any damages whatsoever (including, without limitation, damages for loss of business profits, business interruption, loss of business information, or any other pecuniary loss) arising out of the use of or inability to use this product, even if the Authors have been advised of the possibility of such damages. Because some states do not allow the exclusion or limitation of liability for consequential or incidental damages, the above limitation may not apply to you.\
\b THE ABOVE WARRANTY IS EXCLUSIVE AND IN LIEU OF ALL OTHER WARRANTIES WHETHER EXPRESSED OR IMPLIED.\
\b0 \
Copyright
\f0 1993 Corona Design, Inc. All Rights Reserved.\
Portions Copyright
\f0 1993 Stephen Michael Schimpf. All Rights Reserved.\
\li720 \
\li180 Permission is granted to any individual or institution to use, copy, or distribute this software, provided all of the original files are included unmodified and that it is not sold for profit.\
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