[Ernesto]

I am not sure i am understanding the parameters that should be entered in the location window:
Longitid, Latitud, day, Month, Hour, Minutes, Seconds and GTM offset.
My concern is about GTM offset.
As far as i understand the concept, this is the "distance" measured in hours, from the Grenwich Meridial to the desired location, in other words it is the Longitud of the desired location, expresed in hours instead of degrees.
If so, it seems redundant with the Longitud and Latitud coordenates.
I thought that I should use Latitud and longitud, or GTM offset, not both parameters at the same time....
I am sure i am missing something but cannot see what is it.
Any explanation will be greatly appreciated!

Ernesto

[Mihnea Balta]

The GMT offset cannot be computed from the longitude using a formula. Many countries use a different timezone than what would naturally correspond to their geographical location due to political reasons. Even inside a single country you can have anomalies - for example, some US states span two geographical timezones, but obviously you want everybody inside the state to be on the same time, so they use a single GMT offset.

Things are made even more complex by daylight saving time. Not all countries use it, and those who do, do not switch to it all at the same date. Things can get messy even inside the same country: most of the US uses DST, but Arizona doesn't except in a small area.

All this means that if you want accurate sun direction based on location and date, you must know either the local time and the GMT offset for that location at that date (including DST), or use the UTC date and leave the GMT offset to 0 (UTC/GMT do not take daylight saving into account).

[Ernesto]

Oh, thanks Mihnea Balta.
this is more complex than I thought!
Ernesto