Tag: GPS

Polar Asterisms

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Have you ever seen the North star, Polaris? It’s decently bright and very close to the North celestial pole.  Lining up with the rotation axis of the Earth, the North celestial pole is the point in the sky that never moves, day or night.  If you know how to find Polaris, it becomes easy to find the cardinal directions and navigate by the stars. And finding it simply requires finding the big dipper, a bright and easily recognizable object.  The same rules apply in the southern hemisphere.  But even though there is no southern star, there is another fantastic object in the South that can guide you to the...

Precision and the Prime Meridian

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The Prime Meridian is the imaginary line of zero longitude, the geographic starting point for any East-West degree measurement of any place on the Earth.  It was selected by an international delegation that convened in 1884 in Washington, DC.  It’s a North-South imaginary line that run right through the Airy transit circle at the Royal Observatory in Greenwich, England.  This is also where we get the measurement of Greenwich Mean Time (GMT). As our ability to measure position and time improves with the Global Positioning System (GPS), the precise position of the prime meridian has actually changed, moving 102 meters East...