Plotting a Planet on the Star Finder
If no star appears on the star base at the observed altitude and azimuth, perhaps a planet has been observed. Because their apparent positions relative to the stars change, planets are not shown on the star base. They may be plotted easily, however, by using the special red template mentioned earlier.
STEP 1
Example, For the 17th of March 1981 extract the sidereal hour angle (SHA) of the planets from the daily page of the Nautical Almanac (Located on the left-hand daily page in the bottom right hand corner). Round off to the nearest whole degree. Find the body's right ascension (RA) by use of the formula RA = 360 - SHA of the planet.
STEP 2
Find the declination of each planet using the 8hours of GMT on the 17th Round off to nearest whole degree .
STEP 3
To plot the Planets, we will plot Venus first, then the others. Place the special RED template over the star base. Just like the blue template north to north. Align the arrow on the template with the graduation at the edge of the star base so that the arrow corresponds to the Venus'
RA - 353°. The template has an open slot with declination graduations along one side. Plot the planet at its declination. measuring from the zero mark toward the center if both the pole and declination have the same name (north or south). or away from the center if they have contrary names. In this case. go 5° south and put an X or dot and label it with Venus.
STEP 4
Next Mars, aline the arrow on Mar's RA of 10 degree. Then in the open slot measure off the declination 1 degree S. put an X or dot and label it with Mars.
STEP 5
Now do the same for Jupiter. aline the arrow on Jupiter's RA of 187°. Then in the open slot measure off the declination 1 degree S, put an "x" or dot and label it with Jupiter.
STEP 6
Last, Saturn, aline the arrow on Saturn's RA of 188 degree. Then in the open slot measure off the declination 0° S, put an "x" or dot and label it with Saturn.
STEP 7
Notice that Jupiter and Saturn are almost on top of each other. Then remove the red template, and place your blue template on. Aline to LHA Aries 260 degrees. The planet's approximate altitude and azimuth may now be read from the star base in the same manner as stars. Periodically. the positions of planets must be re-plotted as time passes.
