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Who would have guessed that the knowledge of how to identify your position based on sighting of the stars could eventually allow us to find our hotel on a business trip? This information journey began with man studying the stars and discovering they were pretty stable in the sky, and that if we account for the movement of the earth, we could reverse the process and find ourselves by looking at them. The auto GPS borrows heavily from the history of navigation.

Navigation has been an important science for mankind since before all continents were discovered. Since the oceans cover the majority of the earth, sailors needed some way to discern where they were once they had lost sight of land. Necessity being the mother of all inventions, the idea of discovering where they were on the ocean surface could be determined by sighting known stars in the sky.

The actual method by which that is done is considerable more complex than many recognize. The science depends on several entering arguments; a relative position of an observer, a horizon, and the known star. Fortunately man has been recording and studying the stars since the early Greeks, so their position for any given day and time are known. The relative position of our observer is determined by dead reckoning, which works by itself well enough for the Portuguese to make it back and forth to the new world.

What makes the north star special for navigation, is that when the elevation can be accurately measured, its elevation in degrees is the same as the latitude of a person making the sighting, eliminating a lot of calculation. The use of a periscopic sextant for aircraft has continued to the present time in some military aircraft, and while it is not as accurate as newer methods, it can still be accomplished if your aircraft loses power or the computers fail.

The solution arrived at was the periscopic sextant, used up to and including the present day in military aircraft. The device is pushed physically through a portal in the top of an aircraft and locked in place to a mount that has an azimuth. It has a small bubble to help hold it level, and the star or sun is sighted through a two power telescope, with filters for the sun, of course.

Day celestial navigation is actually less accurate, because the computations will only yield a single line of position. At night, the use of three stars selected at nearly 120 degrees of azimuth apart will yield three lines of position which form a triangle. Executed carefully, night celestial positions can plot out in a chart with all three lines crossing in a pinpoint fix.

The need for ever greater accuracy as aircraft became faster and the navigational routes became more crowded drove the invention of more accurate devices. The advent of the inertial navigation system nearly spelled the end of using a periscopic sextant because it was even more accurate and required little human input to work. As long as its accurate position was input and its gyroscopes properly calibrated, it used motion detection to track aircraft movement in all directions.

The final step in navigation progress came about with the satellite era. Since these man made celestial bodies have known positions and can be programmed to transmit signals with that information, a receiver on earth can determine the position it is anywhere in the world. Add computer overlaid maps and you can find your way road by road to places you have never been to before.

Kim Logan likes to use the best auto GPS when she is on the road. She is a successful computer hardware salesperson and she attributes her success to the best auto GPS unit for getting her everywhere on time. She owns an auto GPS reviews blog where she lists her recommendations.