From: David Pike
Date: 2021 Dec 8, 06:30 -0800
Working through the examples in Rantzen’s Little ship Astro-Navigation has inevitably required me to refamiliarize myself with the Nautical Almanac, a publication I’ve always irreverently thought of of as an Air Almanac for purists. This of course reintroduces the mysterious ‘v’ correction at the bottom of the Planet Columns on the Daily Pages. Please confirm if I’m understanding this correctly.
1. Because the GHA times in the Daily Pages of the Nautical Almanac are one hour apart, there needs to be 30 pages of Increments and Corrections (I&C) (two minutes on each page from 0-59 minutes) to achieve GHA to the nearest second. An Air Navigator (AN) only has to add 15’ per minute and ¼’ per second to the preceding ten-minute GHA. Even then, the AN always tries to make mid-time a ten-minute time from the Air Almanac, followed by two more observations after mid-times four and eight minutes after the first observation if going for a 3-star fix. Then the only corrections needed are +1’ and +2’ to the GHAs.
2. If it wasn’t for the ‘v’ corrections, there would have to be 30x365 I&C pages in the Nautical Almanac, because the positions of the planets viewed from the Earth is a bit like a slow foxtrot (SQQS). However, if the values in the I&C section are adjusted for ‘v’, which varies for each planet throughout the year, the I&C section can remain at 30 pages of basic corrections. DaveP