Lab Polaris Observation for Azimuth

Objective:This lab will familiarize the student with procedures for determining the true azimuth of a survey line by star observations.

Overview:The horizontal angle from a star such as Polaris ( the North star) is measured at a known instant of time to a survey mark. From the measured time of observation, the azimuth of Polaris may be computed by spherical trigonometry. The survey mark's true azimuth is computed by combining the star's true azimuth with the measured angle,

Field Procedures. Calculations, and Analysis:

1.Measurements: In the field, find a station with a clear view of the northern sky. Set or choose a distinct point for the instrument setup. Set or choose a survey mark about 300 ft away from the instrument.

Calibrate your watch before going into the field. Determine the number of seconds (down to the nearest ½ second) between your watch time and true time. This is the watch correction + or – from observed to true.

Setup the total station. Illuminate the cross hairs with a flash light if the total station doesn't have any internal illumination for night operation. Set zeros and sight the backsight mark. Turn to polaris. Track the star and when the star is exactly behind the vertical cross hair, say MARK. The notekeeper then reads the observation time on the watch. The time and horizontal angle are recorded. Wait a few minutes and then take a second observation. You will calculate two azimuths and see how well they compare.

2. Calculations: Use the spreadsheet to calculate the Star's azimuth Z angle, and then the true azimuth of the survey Mark. Find the GHA and declination of polaris from the BLM Solar and Polaris Ephemeris on website: You may get further info by reading the paper discussing the advantages of using Polaris:

In the spreadsheet, enter the measured values of angle, time, GHA star, Declination star, etc. and compute the azimuth of the survey mark.

3.Precision Check: Calculate the mark's azimuth for both your field observations. Compare the two and analyze the results. Compare with other class members if you are using the same survey line. Are your values reasonable?? Discuss your evaluation of the overall process and results.