Calculating times of sunrise and sunset.
The times of the visible rising and setting of the sun are contained in the daily pages of the nautical almanac. They are tabulated for the middle day of the three on that page and provide the Local Mean Time (LMT) of the rising/setting of the sun on any particular meridian (observer’s meridian). In order to convert the time to zone time, the LMT must first be changed to GMT and then to zone time. The tables are entered with the latitude of the observer. In order to obtain the precise times of sunrise/sunset, one would have to interpolate for the difference between the tabulated latitude and the actual latitude. If for example, the observer’s latitude is 34° 30’ south, one would look up the time next to the lowest tabulated latitude (ie 30° S) and then interpolate between the times for 30° S and 35° S, ie:

Calculating times of sunrise and sunset.

If a bearing of the sun is taken when the middle of the sun is on the horizon, a correction has to be applied to counter the effects of refraction and parallax.  The correction may be obtained from the table in Nories Nautical Tables.  To avoid this correction, the bearing should be taken when the lower limb of the sun is half a diameter above the horizon.