Principles of Celestial Navigation

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

Chief Sheedy: After you obtain your running fix and DR it out, the next thing you do is take an evening three-star fix in the same exact manner as you took the three-star morning fix. And that would conclude your day’s work in navigation.

For our example, let's say there was an ordered speed and course change after the afternoon Sun line was taken. It gives us a DR position of 32 degrees 23.5 minutes north, 55 degrees 44.3 minutes west at time 23:10:25 UT, when we take our evening sights.

sky map showing locations of Altair, Dubhe, and Spica

We will maintain the same index correction (-0.4 arcminutes), and the same dip correction (-3.1 arcminutes). The three stars we observed are Altair, Spica, and Dubhe.

strip form for three-star evening fix with sextant heights marked

The sextant readings are 21 degrees 29.3 minutes; 40 degrees,1.1 minutes; and 41 degrees 33.4 minutes, respectively. Using these, we obtain Ho for each star.