Sunday, December 16, 2007

PLOTTING PLANETS

Plotting a Planet on the Starfinder
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.

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 comer). 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. Find the declination of each planet and round off to nearest whole degree.

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 plants RA.

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.

Next Mars, align the arrow on Mar's RA of. Then in the open slot measure off the declination, put an "x" or dot and label it with Mars. Now do the same for Jupiter, a line the arrow on Jupiter's RA. Then in the open slot measure off the declination, put an "x" or dot and label it with Jupiter.Last is Saturn, align the arrow on Saturn's RA. Then in the open slot measure off the declination, put a "X" or a dot and label it Saturn.

Then remove the red template and place your blue template on. The planet's approximate altitude and azimuth may now be read from the star base insame manner as the stars. Periodically the positions of the planets must be replotted as time passes.