Gentlemen, hope you can help me in this little "predicament."
At first , a few general terms:
1. Apparent time is a measure of the sun' true position. To get Greenwich apparent time at any instant we just convert GHA of the sun into time (hh/min/ec)., We need apparent time to find when the sun will be on the observer's meridian. Local apparent noone, when the observations for latitude are made. We know that it is different for each meridian, and unless two places are on the same meridian- apparent time is different.
2. On the Mercator chart every parallel is expanded in the ration of the secant of its latitude.
To avoid local distortion every meridian of a Mercator chart must also be expaned in the vicinity of each parallel by multiplying it by the secantr of the latitude of the parallel.
My question:
When the vessel is located above let's say 50 deg Lat. and we are trying to find LAN the natural curvature of meridians would make GHA slightly shorter than Mercator chart projections ( straight, parallel lines). And it means LAN calculated would be different from LAN real , considering expansion ratio of scant of the latitude. And it means the moment we are catching the sun in a sextant is not exactly the time the sun is in Zenith. Difference should not be significant, but I just want your expert opinion about it.
Please, advice.
Thank you
At first , a few general terms:
1. Apparent time is a measure of the sun' true position. To get Greenwich apparent time at any instant we just convert GHA of the sun into time (hh/min/ec)., We need apparent time to find when the sun will be on the observer's meridian. Local apparent noone, when the observations for latitude are made. We know that it is different for each meridian, and unless two places are on the same meridian- apparent time is different.
2. On the Mercator chart every parallel is expanded in the ration of the secant of its latitude.
To avoid local distortion every meridian of a Mercator chart must also be expaned in the vicinity of each parallel by multiplying it by the secantr of the latitude of the parallel.
My question:
When the vessel is located above let's say 50 deg Lat. and we are trying to find LAN the natural curvature of meridians would make GHA slightly shorter than Mercator chart projections ( straight, parallel lines). And it means LAN calculated would be different from LAN real , considering expansion ratio of scant of the latitude. And it means the moment we are catching the sun in a sextant is not exactly the time the sun is in Zenith. Difference should not be significant, but I just want your expert opinion about it.
Please, advice.
Thank you