People often write me with comments and suggestions about the Chinese Astrology programs on this website, and by far the most common problem is not to calculate the solar time of birth before entering the data in the form to get your chinese natal chart.
It's easy to assume that solar and civil time (the one showed by clocks) can not be that different, but the truth is what you can see on this map:
|Map made by Stefano Maggiolo|
Basically only the places that appear in white or with very light shades of green or red can have a similar solar and civil time more or less, and then only when they are not using the summer time (DST) which would make just some places coloured in green to match their civil time to their local solar time, and as you can see in the map, most places are red not green!
The areas shown in green on the map have their civil time ahead of solar time, and those in red are delayed, the more intense the color, the bigger the difference.
For example in the case of Latin America clearly stands out Argentina, where standard time is much more delayed than in any other country around them:
Argentina is also a good example of why often is not so simple to calculate the solar time of birth, this country has changed often in the past its time zone, for example until 1969 it was in UTC-4, then between 1993 and 2007 didn't change the time during the summer, and in 2008 resumed changing the time for the summer, but a number of provinces (including Salta, Neuquén and Rio Negro) didn't adopted this change, then since 2009 the whole country returned to UTC-3 with no time change for summer time, with the exception of the province of San Luis, which according to Wikipedia is in time zone UTC-4 and does change the time during the summer.
This is why I'm a bit wary of programs that will calculate your solar time of birth, to do it properly they need a HUGE database where any city or place is related to its latitude and longitude and also to a kind of table which says all of the changes to time zone and DST over the years for every single place in the database, but to create and maintain such a database is such a big job that I guess most programs out there just have an incomplete and outdated database which in many cases can return wrong solar times... so my approach to it is doing the calculations by hand researching the info here and there in a case per case basis.
Another example, now in Europe, in the case of Spain the delay is remarkable, much more than in Portugal or Morocco:
In fact some people theorize that the custom in Spain of eating lunch and dinner later than in the countries around it may be due to this gap between solar and civil time; in other words, people tends to be guided more by the sun than by the clock (when they can).
In contrast, in North America there are many areas where solar time does not differ so markedly from civil time:
As you can see, big cities as New York, Chicago, Denver and Los Angeles have their standard times almost coinciding with their solar times (when not using DST).
And interestingly enough, the place of the world with the biggest difference between civil and solar time is China, the whole country has the same time zone despite being huge and extending from Korea to Afghanistan:
In fact there is some controversy among Chinese astrologers themselves regarding whether to use Beijing civil time for all the astrological calculations or not; there are even those who convert the birth time of those born outside China to Chinese Civil Time to do the calculations.
My opinion on this is that one must always calculate the solar time of birth in the place where the person was born, and this is because astrology is based on the relationship between what happens in the Skies and over the Earth, in such a way that solar time of birth is just a way to indicate the position of the Sun in the place and during the moment the person was born, and obviously what matters is where the Sun was where that person was born, not in Beijing or elsewhere.