This may seem like a rather stupid question, but please bear with me. When did we find out that when it was night in one side of the world it was daytime in the other side. Was it the realization that earth was round that made it?
Yes.
But the standardisation of times across distance occured with the advent of the railways - IIRC it was Brunel, with his Great Western Railway from London to Bristol, that decided the 8-minute difference between the local times was incompatible with his desire for a punctual, reliable service.
The ancient Greek Erasthones’ method for computing the diameter of the Earth entails an implicit realization of the fact. He calculated it by observing the angle of the sun in one city at a moment when he knew it to be directly overhead in another.
As observed, standardized time didn’t come along until the 19th century. Until rail travel, different geographical regions, even down to the municipal level, maintained different solar times, setting their clocks to noon when, well, it looked like it. Nobody thought it mattered much that different places have their clocks synchronized.
This history credits one Sir Sanford Fleming:
http://wwp.greenwichmeantime.com/info/time-zones-history.htm
It’s considerably more complicated than just Brunel, and while Fleming played a large role in the political aspects of getting international agreement, he was just one of a huge number of people who were struggling with the difficulties of time measurement.
Time Lord: Sir Sandford Fleming and the Creation of Standard Time, by Clark Blaise is the standard biography, a light but weirdly scattered book.
Equally odd in its way, but a better overall look at the subject and the difficulties is Einstein’s Clocks, Poincaré’s Maps: Empires of Time, by Peter Louis Galison. The Poincaré half is actually the part about time.
And yes, almost certainly the Greeks understood that the roundness of the earth placed half of it in shadow. The Babylonians and Egyptians might possibly have understood this as well. For info on shadows and the place they have in astronomy and our understanding of the world, try the almost magnificently odd The Shadow Club: The Greatest Mystery in the Universe - Shadows - And the Thinkers Who Unlocked Their Secrets, by Roberto Casati, translated by Abigail Asher.
Do you think the modern world is moving towards everyone being on GMT (Zulu) time, and simply adjusting local scheduals to it?
Nah. With time zones, everyone gets a “noon” that feels like noon, and they go to work in the morning and get home in the evening. There are only a very few applications where it matters (i.e. the military and aerospace), and they’ve already gone to Zulu time. It’s like the metric in the U.S. Anybody who needs it, already has it. Otherwise, why mess with a workable system?
Well only if you can convince us in the Southern hemisphere to go to work in the middle of the night. I vote no.
We quite like being a day ahead anyway and if you ask us nicely we just might tell you what tomorrow will be like.
I would be happy if you Northern hemisphere types stopped pointing out that it is weird to have Christmas in the summer though.
[QUOTE=calm kiwi]
Well only if you can convince us in the Southern hemisphere to go to work in the middle of the night. I vote no.
[QUOTE]
You mean “Eastern hemisphere.” The fact that you are south of the equator has nothing to do with your time zone or date. People in South America have local noon at the same time as people in North America who are on the same meridian.
This placque is at Union Station in DC.
I have way too much time on my hands.
[QUOTE=Dr. Lao]
[QUOTE=calm kiwi]
Well only if you can convince us in the Southern hemisphere to go to work in the middle of the night. I vote no.
See SDMB always fighting ignorance! Now I know where I live 
Bah, preview.
Anyway, somewhere in between the discovery that the Earth was round and therefore when it was day here it was night on the other side and the establishment of time zones, we have John Harrison and the solving of the problem of figuring out ones longitude through his invention of a mechanical clock that worked at sea: http://www.amazon.com/exec/obidos/tg/detail/-/0140258795/104-6434578-0475908?v=glance Clocks at the time either had pendulums or falling sand or dripping water, things that generally don’t work too well on a rocking boat.
Actually, most of Europe is in the Eastern Hemisphere.
I think that what you all want to say is the hemisphere nearer the 180 degree meridian than the prime (Greenwich) meridian.
Or perhaps just say the Pacific Rim.
Right, since we are talking about GMT. Kind of annoying that GMT is right on the line between the eastern and western hemispheres, at least for the purposes for this discussion.
Another (perhaps amusing) point at least tangentially related to the discussion of the spherical nature of the Earth and what it’s like for those on the other side is the millenia-long, theological debate over the existance of antipodes. It may be interesting for all you Aussies and Kiwis that for 12 centuries it was the Christian Church’s official position that your very existance was contrary to scripture. The Earth may be round, they said, but no one could possibly live on the other side.
But is is weird to hear the song “I’m dreaming of a white Christmas” on the radio when you’re down under, which I did when I was vacationing in New Zealand and Australia in December one year! Also weird seeing poor Santa in a store dressed in his standard winter “uniform” instead of something more logical like, perhaps, shorts.
Side notes:
Time difference according to longitude was well-understood long before there were time zones. It’s a key part of celestial navigation. You make observations of the position of the sun at one place (say the Royal Observatory, part of Henry VIIIs Royal Palace at Greenwich, a bit downstream from London). If you always know what time it is at Greenwich, you can check the sun’s elevation above the horizon where you are, compare it to where it’s supposed to be at Greenwich, and figure out your longitude. Until the late 1700s, this trick was nearly impossible, because chronometers couldn’t stay accurate over long periods while out in harsh ocean conditions. When the Royal Navy finally adopted Harrison’s chronometer, winding the thing was a key part of a day at sea.
Standardized time zones within the same political entity evolved in the US. Until the 1880s, exact time didn’t matter all that much. But railroads need it to coordinate schedules and prevent two trains from trying to occupy the same track at the same time. The railroads pushed for time “zones” in which all towns would be on the same time. On average, it works.
Some places in the world are a bit unusual because they’re 1/2 hour off the next neighboring time zone, instead of a full hour. Newfoundland is like this; they’re officially 1/2 hour later than Eastern US time. India is the same way.