purposes. The two stars, called Pointers, which form the side of the Dipper away from the handle, point constantly to the North Star, brightest star in the constellation of Ursa Minor (Little Bear). The Pointers are a great aid to navigators.
The familiar stars and constellations are not always visible from where you may happen to be. You must have some means of identifying navigational bodies when nothing you know by sight can be seen overhead. One method by which you can identify those celestial bodies is to use the Star Finder.
Using the Star Finder
The star finder may be used either to:
1. identify an unknown body whose altitude and azimuth have been observed,
2. make a list of stars and planets available for observation at morning or evening twilight for a fix.
To use the star finder, first determine GHA of Aries (1") for your time of observation from the Nautical Almanac, Next, determine LHA of Aries (1") by subtracting your longitude from GHA
of Aries if in west longitude or by adding GHA of Aries to your longitude if it'! east longitude, Select the template nearest your DR latitude and place it on the northern or southern base, depending on whether you are north or south of the equator. Ensure that the proper side of the template is UP, hence, north to north -- south to south. Rotate the blue template until the 00 to 1800 arrow on the template is over the LHA on the base plate. The stars or planets available to you at that time, will be under the grid system of your blue template. DIRECTLY OVERHEAD (Zenith) then is represented by the cross at the center of the open space on the template,
The sky overhead or dome is now shown in the part of the base covered by the curves on the template. Moreover, the approximate azimuth and altitude of any navigational star within these curves can be found by following the lines on the template,
Finding an Unknown Star or Planet
After a long period of heavy weather, you may see the navigator out on the bridge wing eagerly scanning the heavens, his sextant at hand. He is undoubtedly hoping that the overcast will break long enough for him to have a shot at even a single star.
If the navigator should manage to pull a star down, the star's identity may not be known. This is where one the uses of the star finder comes into play. An azimuth (bearing) of the star should be taken at the instant of observation. When the correct template is oriented properly on the star base, the name of the star can be read at the intersection of the azimuth and altitude lines on the grid.
First, we will look at an unknown star, using a problem for an example.
