I have a screensaver installed on my PC that I really like, which I
think many of you might enjoy as well. It is "Earth.scr", and may be
downloaded from the site http://www.fourmilab.ch/earthscr/ . The Earth
screen saver displays an image of the Earth as it is currently
illuminated by the Sun, from a variety of viewpoints. You can view the
Earth from the Sun (day side), the night side, from the Moon, or from an
arbitrary altitude above any point on the globe specified by latitude
and longitude. Day and night regions of the globe are shown based on the
current date and time. The image of the Earth was developed by the
Marine Geology and Geophysics Division of the National Geophysical Data
Center operated by the United States Department of Commerce, National
Oceanic and Atmospheric Administration, and has some very nice detail.
The screen saver was developed by John Walker, founder of Autodesk,
Inc. and co-author of AutoCAD. The URL for his main site is
http://www.fourmilab.ch/ . This main site is fascinating, and is
definitely worth a visit. His topics include computing, cryptography,
astronomy, mathematics, physics, and even a little science fiction and
humor.
Some of you may also be interested in downloading another program of
his, "Home Planet", which is a comprehensive astronomy / space /
satellite-tracking package for Microsoft Windows 95 and Windows NT 4.0
and above. It allows you to view:
o An earth map, showing day and night regions, location of the
Moon and current phase, and position of a selected earth satellite.
o A panel showing detailed position and phase data for the Sun and
Moon.
o Panel showing positions of planets and a selected asteroid or
comet, both geocentric and from the observer's location.
o A sky map including rendering of spectral types, planets, earth
satellites, asteroids and comets. Celestial coordinates are included.
Precession and proper motion are accounted for in the display.
o A telescope window which can be aimed by clicking in the sky map
or telescope itself, by entering coordinates, or by selecting an object.
o A horizon window which shows the view toward the horizon at any
given azimuth. The horizon can be adorned, if you wish, with fractal
forged terrain and randomly generated scenery, including houses,
livestock, and trees. The scenery is generated by a user-extensible DLL
which allows customisation.
o Orrery allows viewing the solar system, including a selected
asteroid or comet, from any vantage point in space, in a variety of
projections.
o Satellite tracking panel. Select an Earth satellite from a
database of two-line elements, and see its current position and
altitude. Satellite will be shown as an icon on Earth map, Sky,
Telescope, and Horizon windows.
The program has many more features than I can list here.
I hope you find his site interesting.
Pete S.
