Great heavens above. (astronomy software) (evaluation)
by Lamont Wood

Galileo probably would have been the first person to suggest a software program for tracking the heavenly bodies had he only been born a few centuries later. As Galileo, Copernicus, and the rest of the stargazing pioneers knew, you can easily get lost in the night sky. The random spread of stars can defeat any attempt to learn the ever-shifting planetary positions and dozens of star patterns that at first glance look nothing like the constellations they're supposed to form.

In the old days, the undaunted could venture into the night with star-chart wheels showing the stars' nightly positions, usually for the wrong latitude and with confusing orientations. And then there were clouds, mosquitoes, jiggling telescopes, and eventually, an urban sky glow to drown out all but the brightest stars.

Now there's a better way--astronomy software that literally lets you explore the sky during the day--even indoors. You can learn the sky and solar system as if they were your own neighborhood, which in a way, they are.

Here we'll take a look at several leading astronomy packages for the PC. Each package was examined on a 16-MHz 386 machine with a VGA monitor. No coprocessor was used. First let's go over some basic terminology.

Positions and sizes in the sky are measured in degrees, where a degree is about the width (no length) of your index finger at arm's length. Brightness is measured on a magnitude scale, where 1 is about as bright as any star gets and 6 is about as faint a star as you can see on a very dark night without a telescope. The programs ask for your location in longitude and latitude, not only to figure rising and setting times, but also to calculate the appearance of solar and lunar eclipses. You're also urged to use a coprocessor to speed up orbital calculations.

For the beginner, EZCosmos from Future Trends seems like the best bet at $69.95. The screen shows the sky as it would look if you were on your back with your feet to the north. Placing the cursor on an object and pressing Enter will bring up identifying information about the object. Additionally, there are screen graphics (in the CompuServe GIF format) of 41 objects, including the planets and prominent galaxies and nebula you can call up. (Alas, for the beginner who might be misled, these are time-lapse photos taken through a big telescope--more colorful and detailed than what you would see through a backyard telescope.)

EZCosmos finds and displays named objects and allows you to speed up the pace of time and watch the planets move against the stars. (At intervals, Mars actually stops and moves backward.) Also, you can focus on the sun and watch for eclipses.

While this program does make it easy to take a grand tour of the universe, it isn't for the serious backyard astronomer. It doesn't offer stars dimmer than sixth magnitude, and it can't zoom in to a field narrower than one degree--a field twice the diameter of the full moon.

LodeStar Plus II from Zephyr Services ($199.95) at first seemed like the same thing, only it's slower (taking more than a minute to draw the full sky), has a clumsier menu-driven interface, and provides no screen shots of celestial objects. According to Zephyr, it runs slower because things are calculated with more precision. The basic version comes with stars to magnitude 6.5, and there's an expanded version, for about $30 more and 8MB more of disk space, which has an SAO (Smithsonian Astrophysical Observatory) star catalog of 270,000 stars that reach all the way to 12th magnitude.

As with EZCosmos, you can place the cursor on an object, have the system identify it, and then zoom in to a specific magnification--this time up to 999.9 powers, covering a field barely one-tenth of a degree in diameter. The only way to get a printout is by pressing PrintScreen, and you need a CGA monitor for that to work.

LodeStar--especially the expanded version--would seem to be best for the serious amateur who wants to plan an observation session or perhaps identify the contents of an astrophoto, cases in which precision matters more than speed.

Meanwhile, The [underscore] Sky 4.1, from Software Bisque, is meant to be used outdoors. Its control menus are shown in red so using the computer won't wreck your night vision. You can point and click your input from an onscreen keyboard chart without having to fumble at the keyboard in the darkness.

The star field in painted almost instantly on the screen--no tedious waits. You can zoom in on anything within view by moving the mouse cursor to the field you want to see and drawing a box and clicking. It was quite a thrill to zoom in on clusters like Pleiades.

The [underscore] Sky will take you down to two-tenths of a degree, where the moon or sun takes up most of the screen. However, only an outline disk is shown; no attempt is made to show the actual solar bodies. You're supposed to look for those yourself through your telescope.

In addition to showing the planets, The [underscore] Sky has a special display to show the positions of the four Galilean moons, a favorite of many backyard astronometers. (Io, Ganymede, Castillo, and Europa, lined up with Jupiter's equator and changing positions nightly, can be seen with a small telescope.) There's even an overhead view so you can identify each moon and its actual location in orbit, which isn't evident from the edge-on view you get from Earth. You can also watch this miniature solar system in action by speeding up the pace--orbital movement is evident even with five-minute increments.

There's also a special eclipse display that shows lunar and solar eclipses for your location. You see the way the moon and sun will move across each other with the times of first and last contact and the times of maximum coverage. Earth's umbra during a lunar eclipse is seen in red--the color the moon actually appears during a total lunar eclipse.

The [underscore] Sky comes in three different packages: AT $75 for Level I, you'll see up to 10,000 stars and deep-sky objects at magnitude 5.5; for $99 you can get the leve II version and see up to 45,000 stars and other celestial objects at magnitude 7.9; Level III, for $175, shows 272,000 stars and objects to magnitude 9.

A telescope-link kit is also available for $699. You mount sensors on the two axes of your telescope, and after you calibrate your telescope's setting on two selected stars, your cursor will point in exactly the direction of your telescope. It's pricey, but with the link kit, you can look at scores of objects in one evening with no time lost due to endless blind searches.

If The [underscore] Sky is intended for the serious amateur astronomer, Dance of the Planets from a A.R.C. Science Simulation is intended for the serious amateur astrophysicist. Priced at $195, it shows the celestial globe and stars therein, but that's incidental.

The opening screen shows a starfield with an unfamiliar bright star in the middle, near the constellation Orion. That's the sun, seen from your viewing position of about 2.5 billion miles out in space. You can zoom in to a maximum magnification of 32,000 and look at individual planets and, with an accelerated time frame, watch them rotate. The software also includes maps of the planetary surfaces. Although Earth and Mars are hardly more than large dots with crude features, Jupiter is big enough for you to watch the Great Red Spot slide by.

You can also switch to an Earth-based view to watch eclipses and events like the apparent merging of Jupiter and Venus fon June 17, 2 B.C. The point of Dance, however, is to pull back into space, arrange the viewing position you like (you can change the angle from which you're looking into the solar system), invoke the command that outlines the orbits, and start the dance of the planets. Everything is visual and obvious, and by the time you're finished with the manual, Kepler's Laws and the geometry of elliptical orbits out to be second nature. The five parameters it takes to defined an orbit will no longer be mathematical gibberish, but self-evident statements.

Dance comes with orbital data not only for our nine planets, but for their 61 satellites (including Pluto's) and for 4650 asteroids and 1300 comets. Pick out a particular comet, track it into the future, and see if Jupiter ever swallows it or vectors it into the sun. You can track 20 orbits simultaneously, although for results anytime soon, you'll want to get a coprocessor.

Dance will even give you a 3-D view of the orbits. The package comes with red-and-blue goggles like the ones used for watching 3-D movies. They work best for examining comet orbits, which are often rotated away from the plane of the planets' orbits. You can make up your own comets, input their orbit parameters, and watch what happens. The only thing Dance left out is a spaceship option so you can figure in the results of acceleration and fuel consumption.

For those of you who wonder what it's fall about, there's also astrological software on the market. We looked at Chartwheels II ($150 from Astrolabe) and found that it does indeed track the positions of the planets. You won't learn astronomy, though, since it's only concerned with the zodiac for casing astrological charts and showing the influence of the planets at a particular moment.

Planets do, in fact, exert influence--gravitationally on each other anyway. Gazing at the results with the help of astronomy software could help open up the heavens for you, if that's what you're after. At the very least, you'll no longe fumble your way through the night sky.

Galileo would approve.