Sun Run Merpass
The procedure is similar to that of sun run sun
1) Starting from a dead reckoning point (DR), calculate the time of merpass at DR.
2) With that time (converted to Greenwich Mean Time :GMT), find out the declination of the sun from the nautical almanac.
3) Find the altitude of the sun at the time of merpass.
4) Find the latitude using the formula : Latitude = 90o - Altitude + Declination
5) Draw this latitude on the chart.
6) Transfer the previous position line to the DR of merpass.
7) The point of intersection between these two lines is the observed position at the time of merpass.
Merpass Run Sun
It is exactly the same as Sun Run Merpass, except that the sequence of events is the opposite.
1) Calculate the time of merpass and note the DR
2) With that time (converted to GMT), find out the declination of the sun from the nautical almanac.
3) Find the altitude of the sun
4) Calculate the latitude with the 2 values of altitude and declination
5) Draw the latitude on the chart
6) With the DR from merpass, drop a perpendicular line on the latitude line to get an intercept.
7) Find the observed point in the usual way stated in Sun Run Sun.
Back to 'content page'
Back to 'Navy Procedure'