Why is the sunRISE (LT) date often different from the sunSET (LT) date when doing an Almanac Body calculation?
This applies to the original 16-bit version (v1.05):
The Almanac Body function in SkyMate Pro provides the instant almanac information
for the time/position that is used for the calculation.
The Rise/Set/Transit calculations are based on the UTC date that is used --- not the LT date.
All Local Time values entered on the tool bar are converted to UTC dates.
The astronomical formulas in SkyMate Pro calculate Rise/Set/Transit values for the selected UTC date.
Results are then displayed in both LT and UTC times.
Depending on your time zone correction the LT displays for the transit calculations will be on different dates, although the UTC calculation will be for the selected date.
Since most of your (LT) Rise/Set calculations will actually occur on two different (UTC) dates,
if you are trying to get the SuRise and SunSet value for the same day, you will need to do a '2nd estimate' calculation to obtain both values.
Do your first calculation to obtain the SR or SS for the current (LT) date.
Reset the Lat/Long DR position to reflect the vessel's new position for the 2nd calculation.
Change the local time so that the UTC date is before/after (depending on your E/W location) from
your first calculation. Recalculate the Almanac to get the 2nd transit infomaton.
This process should provide you with your Rise/Set times for the same (LT) day.
The key thing to remember is what UTC date is being used. You will also find
that when you cross between East/West longitute time zones that the Rise/Set dates will reverse since UTC will be ahead/behind your position.