The Answer Site Format and Use Navigational Arithmetic Lesson 6: Diagram on the Plane of the Celestial Meridian Lesson 7: Sight Reduction, Tabular Resolution Lesson 8: Sextant observations and corrections Lesson 9: Lines of Position (LOP) Lesson 10: The x-Body Fix Lesson 11: Latitude at Local Apparent Noon (LAN), Special Observations Final Exam Problems The "Answer" I find it useful to give people the answer to the big picture before digging deeply into the problem.  That way we all know where we're headed.  That said, here's a several line description of how celestial navigation works.  Refer back to this often. If we can know the exact position in the sky that a body would occupy at a precise moment in time, we can then compute the altitude (height above the horizon) that the body would have from a precise location on the surface of the Earth.  If we measure the actual altitude of that body at that precise moment, we can determine the difference between the altitude from a known position on Earth and the altitude from our actual position on Earth at the same moment in time.  Knowing the difference between those two altitudes allows us to draw an LOP (line of position) on a chart knowing that we are somewhere on that line.  If we complete the same process on a second body, we know with some confidence that we are at the intersection of the two LOPs.  We call that position a FIX. Our job through the rest of the course will be to understand all the variables which are at work when we determine the two different kinds of altitude describe above (computed altitude and observed altitude) and, finally, to learn how to plot LOPs.  This description is necessarily general.  You'll learn lots more detail as we go.