Few Words about GPS

When Celestron and Meade first began integrating global positioning system (GPS) receivers into their SCT mounts about 10 years ago, amateurs were plenty excited. We imagined GPS would take the last of the drudgery out of telescope setup: no more sighting go-to alignment stars, no more polar alignment headaches. Reality turned out to be a little different. Onboard GPS receivers did and do help some but not to the extent we thought they would.

GPS can be a considerable labor saver with fork-mounted telescopes set up in altazimuth mode, but it does not work alone. Yes, Meade and some Celestron forks can find north, level themselves, and head for go-to alignment stars without much user intervention. The observer still has to center the alignment stars, however. And, GPS alone could not even do this much. A GPS-enabled fork-mount scope must also be equipped with level sensors and an electronic compass to do its roboscope thing.

In equatorial mode on a fork or when used with a German equatorial mount (GEM), supplying accurate time, date, and position information is all a GPS receiver does. It does not polar align the scope, and it does not help the mount when slewing to alignment stars. Look on GPS as a timesaver for equatorial mode and nothing more. Paying extra for the minor convenience of not having to manually input time and position does not really seem worthwhile, but the manufacturers must believe amateurs want that since almost every GEM mount has GPS available at least as an option.

Some amateurs wonder if the go-to alignments produced by GPS scopes are more accurate than those produced by non-GPS scopes. The answer is "no." Accurate time, date, and location may help the scope come closer to go-to alignment stars during its initial slews, but it will be no more accurate than a scope with date, time, and location entered manually with reasonable care. Amateur-grade mounts are simply not able to take advantage of the precision time and location data offered by GPS.

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