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Learn the stars at your computer

Jan 1, 2003

I have a confession to make. I have a hard time identifying stars. Why? Well, I do live in San Francisco, where between the fog and the street lights you rarely see the night sky, and it's worse in summer.

So how do I navigate? Well, H.O. 249 gives a pretty good idea where to look for stars. That's almost always worked for me. The plastic wheel starfinder also works, although I have never really been able to visualize the sky from a flat disk. No problem. Plug in the LHA for Aires and you get altitude and azimuth. Knowing that is usually good enough early in twilight for first magnitude stars.

All of this is fairly low-tech stuff. In a way, that is perfectly consistent -- after all, celestial navigation is pretty low-tech itself. But if you want to talk to your on-board computer about it, here are some ideas. First of all there is a Davis Instruments product, PC AstroNavigator. It has, effectively, a self-calculating almanac. Give it a location, date, and time, and it will give you the altitude and azimuth of available navigation stars. To this extent it is similar to H.O. 249. PC AstroNavigator is an old program and therefore will run on very simple hardware. It requires at least DOS 2.1 and 256k RAM. It is packaged with both 3.5-inch and 5.25-inch diskettes. It goes further than simply star finding. It also will do sight reduction, graph lines of position, and even graph DR. Now, as you can imagine, the graphics are very simple. And forget point and clickthis is a purely menu-driven program.

Next stage up is a Windows shareware program: SkyGlobe. It is a bit like a flat, wheel-type star finder, only projected on the computer screen. The sky is projected based on the date and time carried in your main menu. Location is selected from a menu, and is therefore limited to the cities shown. On my laptop, the cursor is a bit hard to see in daylight. Also, the field of view is rather wide, so that the view of the sky is small- scale. With subdued light the display is not hard to read. One of the neat things is that the location of the cursor, in altitude, azimuth and declination, is continually reported in a box display. In the same box there is a message as to whether the cursor is on an object, what the object is, and, if a star, its magnitude and right ascension. Major stars and planets are labeled on the display. This is a nice little planetarium, attractively priced. It is available through KlassM Software (1-800-968-4994).

One of the best planetarium programs is Starry Night, by Siennasoft (www.siennasoft.com). It shows a very realistic sky. Although you can click on objects to identify them, there is no printing on the display. The screen can be overprinted with an altitude and azimuth grid, path of the ecliptic, or galactic grid. The default field of view is 100°, which, again, is quite realistic. The field of view can be zoomed to show one minute of arc and centered on an area of sky defined by right ascension and declination to the fraction of a minute. The foreground defaults to grass and trees, but a somewhat imaginative sea scene can be selected. Location is selected by latitude and longitude. Date and time are taken from the control panel. Time can be run forward or backward. As time passes, the program shows twilight, sunrise, the rise and fall of the sun through the sky, sunset, twilight, and night again.

If the sky view from your position is not interesting, then it can be clicked off, or you can change your position to anywhere on earth or to an altitude of a few hundred or thousand kilometers. And if that doesn't do it for you, choose an astronomic unit. Try the night sky from Pluto, sunset on Mars, or noon on Mercury.

An early version can be downloaded from the Siennasoft website. The fancier version is on a medium-priced CD. Both Mac and Windows versions are available.

If your curiosity still isn't satisfied, check out www.seds.org/billa/astrosoftware.html for more titles. Some of these include Skymap, Earth Centered Universe, Deep Space, Home Planet, Cybersky, Redshift 2, Distant Suns, Megastar, Hypersky, Atlas du Ciel, and more. Most of these, from their samples, appear to resemble SkyGlobe in their displays, but they have more tools, can zoom, and so forth. A telescope drive option appears to be standard on the better programs. The Rolls Royce of astronomy programs is the Palomar collection, which costs more than $200definitely for astronomers. With the exception of SkyGlobe, prices run about $100. Of course, only the Davis product has any direct navigation function.

But, hey, for those of us who live between rain and fog, it's nice to see the sky somehow.

Chuck Warren is a sailor and real estate appraiser who has voyaged extensively in the South Pacific.