# Celestial Navigation Basics Land Sea & Air – Course_b

## Introduction

In the previous post I described how I developed an interest in Celestial Navigation. This past summer of 2020 it provided an anchor for me to forget about the pandemic and all the horrible consequences that ordinary people suffered and continue to suffer as a result. I made a series of posts/videos on using a sextant. In this post and the following ones I will summarize the important points needed to understand CelNav:
*Why CelNav is still important
*Geographic Position & Nautical Almanac
*Trigonometric Solution of Navigational Triangle
*Sextant Measurements & Reduction Hs–Ha–Ho–Hc–Intercept–Fix
*Manual Methods of Sight Reduction NAO, AP3270
*On Line Course starts Feb.3

## Why CelNav is Still Important

One might easily ask why study CelNav when there are satellite navigation systems that can give our position within meters whereas CelNav can at best give us our position in 100s of meters if not Kms. The pandemic is an example of how something totally unexpected changed everything overnight. Satellite systems are expensive and complicated. A solar X flare or other atmospheric disturbance could knock out these systems. CelNav always can supply a backup. The planets/stars are there and not going anywhere. I am sure that new systems will be developed using electronic sextants that take multiple measurements of the planets/stars and give comparable results to GPS. The mathematics of CelNav is very useful in other fields such as HF Telecommunications and Space Travel. In a recent video two large freighters collided in the Welland Canal, both crews oblivious to what was happening. CelNav forces an increased situational awareness which can be dulled when you stare at a digital display all day.

## GP Geographic Position

GP Geographic Position is probably one of the most important CelNav concepts. At any point in time, a line drawn between the center of a Celestial Body and the center of the Earth passes through the Earth’s surface at the GP. Astronomers are able to calculate the GP for the Sun, Moon, Planets and Navigational Stars and list these points in tables in the Nautical Almanac. The Portuguese/Spanish developed the first Almanacs that we know of and thus were able to sail all over the planet in the 1500s.

Figure 1 shows a plane passing through the centers of the CB & Earth and the Observer on the surface of the Earth. Since the CB is infinitely far away from the Earth (the Moon is an exception), a ray passing between the CB center & Earth center will be parallel to a ray arriving at the position of the observer C on the surface of the Earth. Hc is the angle between this ray and the Observer horizon. (90deg – Hc) is known as the Zenith Distance and is subtended at the Earth center due to the parallel rays. The Great Circle Distance AC = Zd in radians, or AC = Zd*Re where Re = Earth Radius = 6371Km.

Celestial Navigation Basics & Equipment Course: