Lesson 5  Nautical Almanac  
LESSON 1 
The
Nautical Almanac is an ephemeris, that is, a set of tables which
provides us with the positions of celestial bodies throughout the year.
Using the Nautical Almanac, we can determine the GHA and declination of the sun, the moon, and four planets for any second of the year. We can also determine the GHA of Aries, and, thereby, the GHA and declination of fiftyseven navigational stars. There is lots of other information in the Nautical Almanac, some of which we'll use later. White pages The white pages provide us with GHA and declination information for the sun, moon and planets based upon UCT (Universal Coordinated Time, or Greenwich Mean Time). Yellow pages (Gray edged pages) The yellow pages (gray edged pages in the Commercial Edition of the Nautical Almanac) provide tables for the determination of incremental change in GHA and declination for fractional parts of hours (minutes and seconds). By applying incremental change to the GHA and declination found for the most recent full hour of the body, we can determine GHA and dec to the nearest second. Example On December 3, 1997, at 05 hours Universal Coordinated Time (GMT), the sun had a GHA and declination of 257degrees 34.0 minutes. Twelve minutes, 39 seconds later, the sun had increased GHA by 3 degrees 09.8 minutes of arc. Adding the two, we find GHA of the sun at 05h12m39s to be 260 degrees 43.8 minutes. Little d, rate of change of declination, is 0.3 minutes/hour on December 3rd. The 12 minute yellow page (or gray edged page) shows us that the incremental change in declination, the d correction, based on this rate of declination change, is 0.1minutes. Since declination is increasing (growing numerically larger) in a southerly direction on December 3rd, the declination increment is positive and is, thereby, added to the declination for 05 hours. The declination for the sun at 05 hours on December 3rd is S 22 degree 06.0 minutes. Adding 0.1 minutes of declination yields a declination of S 22 degrees 06.1 minutes at 05h 12m 39s. On December 3, 1997, at 05 hours Universal
Coordinated Time (GMT), the sun had a GHA and declination of 257^{o}
34.0. Twelve minutes, 39 seconds later, the sun had increased GHA
by 3^{o} 09.8
minutes of arc. Adding the two, we find GHA of the sun at 05h12m39s to be 260^{o}
43.8. Little d, rate of change of declination, is 0.3/hour on December
3rd. The 12 minute yellow page (or gray edged page) shows us that
the incremental change in declination, the d correction, based on this
rate of declination change, is 0.1. Since declination is increasing in a southerly direction on December
3rd, the declination increment is positive and is, thereby, added to the
declination for 05 hours. The declination for the sun at 05 hours on December 3rd is S 22^{o}
06.0. Adding 0.1of declination yields a declination of S 22^{o}
06.1 at 05h 12m 39s. GHA 12m39s 3^{o} 09.8
Have fun, and if you don't understand something, use the discussion board or mail navigator@cyberacademy.org.
