sun goes up in the east right? and then where is Sao Paulo located? to the east of Buenos Aires. How come the sunrise is later in sao Paulo than Buenos Aires?? shouldn't it be the opposite?
Remember - the days are longer in the summer and shorter in the winter - also the AMOUNT by which that change happens depends on how far north or south of the equator you are. When you're on the equator, day and night lengths are somewhat similar summer and winter - but at the poles, the days can stretch to weeks long!
So sunrise time is determined by both your latitude AND longitude (and also your altitude if we're being picky). Governments impose "time-zones" and daylight savings tricks to roughly get sunrises and sunsets to be at sensible times - but often they botch it...so it's better to do all of your comparisons in GMT. It always confuses me when I call home to the UK from the USA because the time offset is usually 6 hours - but is either 5 or 7 depending on who turns on daylight savings time on what day of the year!