Under The Microscope

DANCE OF THE PLANETS; Arc Science Simulations Software; 1992; $395 + $10 freight + GST. Distributed in New Zealand by Craftware Computing, Tawa.

System requirements (IBM): 80x86, DOS 3.X, 640K, EGA/VGA, HD.

Installation is straightforward and relatively idiot-proof, and the program itself assesses the host machine's hardware for its needs. For use on an IBM-compatible machine, the documentation recommends a numerical co-processor, which, although not essential, certainly adds to the speed and ease of use.

The controls seem a little unusual at first, and there is a tendency for the program to ignore key presses when operating without a co-processor. However, after a short time familiarising myself with the menu layout, it turned out that much of my problem was due to the large number of different functions available.

The manual has a very brief description of the main commands, which is a little too minimal to be of any great use, meaning you have to read the whole thing. It does, however, give a large number of clear examples on how to operate the various functions, along with a variety of examples of interesting events such as the near-capture of comet Gehrels by Jupiter in 1977. The program will simulate this event from any desired angle, by loading the orbit parameters for the comet and then stepping through the approach.

There is a supplied database incorporating around 5,000 asteroids and a large number of comets. Usefully, this database is in text form, permitting any object for which the orbit parameters are known to be loaded into the program. Once such information has been loaded, it is possible to track an object's motion and to observe occultations and close approaches. The database also tracks "deep space objects" such as radio sources or quasars, which can also be checked for occultations etc.

Dance has two ways of viewing objects in the solar system. Either the view is that of an Earth-dwelling observer, or it's from "outside", looking in from an apparent distance of 290 Astronomical Units. Either way, the program gives a most impressive simulation of the major planets. It even shows the Red Spot.

This sort of attention to detail makes the program both a pleasure to use and a useful tool for teaching work. The entire feel of the program is very natural, providing views at the sort of scale where constellations are easily recognisable, or zooming to the sort of scale of early Voyager photos.

There is a persistent desire to increase magnification or simulation speed just beyond the allowable parameters of the program -- not unlike the sort of problem astronomers experience when contemplating more powerful telescopes. To get the sort of detail that would finally satisfy this sort of desire is beyond even the most extravagant programs. For the meantime, Dance is the best compromise I've seen between size and detail, and speed and hardware requirements.

Alex Wynne