02-05-2021, 02:51 PM
Rumata,
My thought is that the moment of LAN as observed in your sextant is correct but this must be qualified by the following;
- Sextants and ship movement combine to effect imprecise determination of LAN.
- Making a series of observations before MP and after MP based on equal altitudes will mitigate inaccuracies but not exactly. Equal Altitudes, of course, will give you longitude and an imprecise latitude. Plotting these observations and then drawing a curve through them can provide a fair assessment of latitude.
These things kept in consideration, a plot isn't necessary to determine LAN- just get zenith and do the calculations to obtain latitude.
See here- https://thenauticalalmanac.com/Formulas....e_Latitude
Yes, the lines of longitude converge is a problem which can be accounted for by adjusting the amount on the UPS (Universal Plotting Sheet) between the lines of latitude. At 50°, as you mentioned, it's not that much....but it is an amount that can be easily measured. Again, this isn't a problem of determining LAN- it would be relative to determining longitude.
Oh, the UPS, generally, is only laid out in 1° lines of latitude and, of course, 1° lines of longitude. And at the Poles it's a real mess since the lines of longitude are so close on the UPS.
Anyone have another idea?
Paul
My thought is that the moment of LAN as observed in your sextant is correct but this must be qualified by the following;
- Sextants and ship movement combine to effect imprecise determination of LAN.
- Making a series of observations before MP and after MP based on equal altitudes will mitigate inaccuracies but not exactly. Equal Altitudes, of course, will give you longitude and an imprecise latitude. Plotting these observations and then drawing a curve through them can provide a fair assessment of latitude.
These things kept in consideration, a plot isn't necessary to determine LAN- just get zenith and do the calculations to obtain latitude.
See here- https://thenauticalalmanac.com/Formulas....e_Latitude
Yes, the lines of longitude converge is a problem which can be accounted for by adjusting the amount on the UPS (Universal Plotting Sheet) between the lines of latitude. At 50°, as you mentioned, it's not that much....but it is an amount that can be easily measured. Again, this isn't a problem of determining LAN- it would be relative to determining longitude.
Oh, the UPS, generally, is only laid out in 1° lines of latitude and, of course, 1° lines of longitude. And at the Poles it's a real mess since the lines of longitude are so close on the UPS.
Anyone have another idea?
Paul