Celestial Workshop

Last Saturday, I attended the field workshop for my Celestial Navigation class. Each class so far focused on the concepts and procedures of calculating your fix based on sextant shots given to us by the professor. Now for the first time, we were to take the sextant shots ourselves. I brought a Davis plastic sextant loaned to me by my good friend, Tim Brown.

We gathered out a Cherry Creek reservoir where the Victoria Sailing School fleet is kept. During the first part of the workshop, we learned how to adjust the sextant so it would work properly. We then began taking sights of the sun.

Working in teams of two or three students, the process began by taking about 10 shots as the sun was climbing in the morning sky. We then plotted the angle of the each shot over time on graph paper. We drew a line through the plotted points and chose the point closest to the line for calculation using the HO249 tables. This yielded our first line of position on a Universal Plotting Chart.

The only remaining step was to wait for the Noon shot when the sun was the highest it would get in the sky. It turns out that with daylight savings time the Noon shot was almost exactly at 1 pm. We then entered the Height of Sextant (Hs) angle in the HO249 tables to yield our latitude.

With our latitude found, we plotted two lines of position on the Universal Plotting Chart and obtained a fix. I am proud to say (tongue in cheek) that we located the Cherry Creek to within 30 miles! This was pretty good, especially as a lesson in how small errors during the calculation can multiply into big discrepancies in the final fix.

I am off to another Celestial Navigation class tonight. Only three more left before the exam, so I better start paying attention!