USING POLARIS AND OTHER CELESTIAL OBJECTS TO ESTABLISH PRECISE GEOGRAPHIC NORTH AZIMUTH WITH THE TOTAL STATION

The determination of precise geographic north direction during field surveys can be difficult in remote areas. A Total Station is very precise in the measurement of horizontal and vertical angles (+/- 5 arc seconds), however, it has no organic capability to resolve the GN azimuth angle. During the instructional design phase of a Geology Field course a method was sought for utilizing a Total Station with celestial observations to efficiently establish an accurate GN azimuth for large scale (1 inch = 10 feet) mapping surveys. Surveyor’s manuals describe how Polaris may be used to calibrate a Total Station to GN utilizing online published ephemeris tables of the upper/lower culmination points. This method requires waiting to observe one of the culmination point times during nighttime - often occurring at inconvenient times. The culmination points are those times when Polaris is directly above or below the celestial pole (CP) as it rotates around the pole in a 24-hour cycle, therefore, back-sighting on Polaris at those times aligns with GN at the precision of the Total Station. Our method is a variation on this method – we track the horizontal and vertical angles of any convenient star for a 4-6 hour period beginning at dusk. Because all stars rotate around the CP in a small circle path, a statistical method to fit a least-squares conical surface through the observation points of azimuth and vertical angles yields the cone axis attitude with a trend component equal to the azimuth of GN. “Zero”-setting the Total Station to this azimuth aligns the instrument to GN. This method will be tested with a variety of celestial objects with statistical results presented at the sectional meeting. This method also provides the ability to precisely measure magnetic declination to test geomagnetic field models, and also provides student with important fundamental knowledge in surveying and astronomical techniques.