A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Axcel B.
Date: 2016 Sep 23, 13:21 -0700
I have a question and don't know if this is actually the right forum but since I don't know where else to post this question, I am going to try it here on NavList:
I was wondering why the Nautical Almanac does not use a v-Correction for the Sun. The Sun's average motion is obviously 15°/h but the True Sun's rate varies slightly throughout the year. So does Venus for instance (and can even move "backwards" with respect to the Sun) but with Venus we use a v-Correction. Why not with the Sun? The position of the True Sun is accurately given for every full hour in the Almanac but when using the Increments we are always assuming a speed of 15°/h which most of the time is not the actual speed of the True Sun. I was comparing GHA values between two consecutevie hours and found that the difference can be up to 0.3' (by applying an Increment of 60min to the GHA of the full hour and compare it with the tabulated GHA value of the consecutive hour). This means that one could get an error/difference in the Sun's position of 18 seconds - isn't it? Is this generally acceptable for purposes of Celestial Navigation and that's why we don't use a v-correction for the Sun?