Principles of Celestial Navigation

A Day in the Life of a Navigator » Three-Star Fix, Evening » Plotting the Evening Three-Star Fix

Chief Sheedy: All right, I cleaned up the Universal Plotting Sheet, and at time 19:35 we have a running fix with our circle around it. I DR’d to the top of the hour, 20:00, 21, 22, 23. At 23:10 we took an evening three-star fix. The first star I’m going to plot is Altair. The azimuth of Altair was 92 decimal 9. From our 23:10 DR position, I’m going to draw an arrow to GP. In this case, it was 3.5 miles towards. Make a perpendicular line, and this is our line of position, 23:10:25 label Altair.

The next one is Spica. 214 decimal 1 azimuth to our GP. Mark arrow, GP. 11.2 towards, make a perpendicular line. Label properly: 23:10:25, Spica.

The last one is Dubhe, 326 decimal 1. And it’s 5.1 away. Make a perpendicular line. 23:10:25. Dubhe. Mark where the three lines intersect.

screenshot of position plot for evening three-star fix

The resulting fix is 32 degrees 13.6 minutes north, 55 degrees 44.6 west. Now that we have our fix, a new DR is started from this position.

Print the completed Universal Plotting Sheet to compare the solution with the plot you created for the three-star evening fix. If your values do not match the correct answer, you may wish to go back and check your work. You can work through this exercise or any of the sight reductions and position plots in the module to practice and hone your celestial navigation skills.