The Introductory Celestial Navigation Clinic is presented in eight Modules:
Glossary of Terms
The Marine Sextant
Taking a Sextant Sight
Time Keeping for Celestial Navigation
Exercise: The Noon Sight
The following are excerpts from the Clinic
The earth rotates around the sun once every year, but it also spins and makes a revolution around its own axis every 24 hours. When the Earth's circumference is divided into 24 equal sections, each represents one hour of the day's time and occupies 15 degrees of arc.
Figure 1 illustrates that each 15-degree segment is represented on a globe or chart by lines extending between the poles; these lines of longitude are called meridians. Meridians are widest at the equator, and become progressively closer together toward the poles. It is important to understand that lines of meridian are not equidistant at different parts of the globe.
Figure 1: Lines of longitude extend between the poles, and are called Meridians of longitude.
The following illustrates the slight complexity when measuring angles in a 3-D spherical geometry. Here GP is the point whereby the sun would be directly overhead. However our vessel is east and north of GP. Thus the angle Hs that we would measure bares a complex relationship with the latitude and declination. Remember sine's and cosine's from geometry?
The zenith of our position is a point directly north (or south) of the GP. This helps us with the geometry a little because if we could project ourselves around the globe on the same latitude to the longitude of the GP then things would be a little easier. This is a partial secret of Celestial navigation.
The following shows why it is much less complex to take a noon shot of the sun.
When the vessel is on the same longitude as the Sun's GP, the sun is at it's highest point in the sky (for us at the position we are at - at that exact time). And if this occurred at the center of a time zone, then the time would be noon. In this clinic later we'll show how to account for not being exactly at the center of the time zone.
Thanks for viewing the excepts - we're pretty sure you can extrapolate this information into knowing you'll have a full understanding of the theory behind and how to do a noon solar sight to determine your Latitude and Longitude position.
The NauticEd Faculty.
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