Principles of Celestial Navigation

A Day in the Life of a Navigator » Morning Sun Line

During daylight hours, the Sun is used for determining our position. It makes a good navigational object because it is easy to find in the sky and easy to measure with a sextant. However, the Sun will only provide us with one line of position; at least until it moves significantly across the sky, which takes a few hours. Therefore we cannot get a fix with one Sun observation, only a line of position. This is why we call the result a Sun line. Later we will demonstrate how Sun lines taken throughout the day can be combined to obtain a fix, but for now let’s show how a Sun line is taken.

Whenever looking or observing the Sun we must use the proper filters so we do not damage our eyes! Sextants have filters that are swung into place when making a Sun observation.

photo of sextant showing filter for use in Sun observations

A morning Sun observation is routinely taken a few hours after sunrise. The reduction procedure is very similar to that of stars, except we must note f we observed the upper or lower limb. A strip form includes all of the steps in the reductions.