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Chapter 9
Celestial Observations and Sight Reduction Methods
Introduction
In this chapter you will learn the methods that are necessary to complete
a day’s work in navigation. These include several ways of finding
gyrocompass error, reducing sunlines and moonlines, finding latitude by
LAN or Polaris, and reducing sights of stars and planets.
We’ve already covered the basics of celestial navigation in chapter 6.
You may want to occassionally refer back to that material to have a
clearer understanding of this material. We will discuss the procedure
aspect of performing and reducing celestial observations only. As you
become more familiar with this subject, you are advised to increase your
knowledge by studying references such as Dutton’s Navigation and
Piloting and Bowditch Pub No. 9.
Objectives
The material in this chapter will enable the student to:
Determine gyrocompass error by azimuth of the Sun and Polaris, and
amplitude of the Sun.
Reduce sights taken on the Sun, Moon, stars, and planets using H.O.
229, Sight Reduction Tables for Marine Navigation, and the Nautical
Almanac.
Reduce sights taken on the stars using H.O. 249, Sight Reduction
Tables for Air Navigation and the Air Almanac.
Determining latitude by local apparent noon.
Plot celestial LOPs based on assumed positions.
Azimuth of the Sun
Topic
Page
9-2
Azimuth by Polaris
9-11
Amplitude of the Sun
9-12
Celestial LOP
9-16
Using the Sextant
9-18
Altitude Corrections
Reducing Sunlines Using Pub 229
Plotting LOPs
9-19
9-24
9-28
Advancing LOPs
9-29
Reducing Sights using Pub 249
9-32
Latitude by LAN
9-36
9-1
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