To Calculate Directions With Sun Shots and Star Shots

Sun shots calculate a direction using solar observations by the hour angle method and use a multiple foresight method. Star Shots calculate a direction from Polaris or a star observation by the hour angle method and use a single foresight method.

1. Click Analyze tabGround Data panelSurvey drop-downAstronomic Direction Find.
2. In the Calculation Type list, select either Sun Shot Calculation, or Star Shot Calculation.
3. Under Observation Station Data, specify the following:
   • Station Point
   • Backsight Point
   • Station Latitude
   • Station Longitude
   • UT1 Time (Sun Shots only)

   See Astronomic Direction Calculator Dialog Box

4. Under Ephemeris Data, enter the following:
   • GHA 00 Hours
   • GHA 24 Hours
   • Declination 00 Hours
   • Declination 24 Hours
   • Sun Semi-diameter (Sun Shots only)
   Note: Enter zero (0) if you are sighting either the center or both the trailing and leading edges of the sun. The left edge is always the leading edge at latitudes greater than 23.5 degrees north and greater than 23.5 degrees south. If only the left edge is being sighted (left when facing the sun), then the semi- diameter is positive; likewise, the semi-diameter is negative when only the right edge is sighted.
5. Click to create an observation set. Enter Direct and Reverse observations for the Backsight Observation, Sun Observation or Star Observation and the Stop Time.

   The observations determine the true astronomic direction from the first setup to the backsight. When you enter the stop time for an observation, the observed and average directions are calculated automatically.