At 12:00 PM GMT (UTC), the shadow of a vertical object on the prime meridian, such as at Greenwich, England, points to one of the poles of the earth, if there is a shadow. The Sun is said to be directly overhead, although in the latitudes north of the Tropic of Cancer or south of the Tropic of Capricorn are never directly “under” the Sun; a line from the center of the Earth to the center of the Sun never goes through Greenwich, for example.
One hour later, one twenty-fourth of a day later, the Sun is “over” a longitude one twenty-fourth of the way around the world. There are 360 degrees of longitude; the Sun is said to be “over” 15 degrees W. 2:00 PM UTC, 30 degrees west. 6 PM GMT, 90 degrees west. 6 AM GMT, it was at 90 degrees east. And at midnight UTC, the sun is exactly around the world from the prime meridian.
Back before railroads tied our worlds together, “noon” where you were was whenever the Sun was “overhead.” It was as long since sunrise as it would be until sunset, assuming there were no mountains for the Sun to hide behind, rising or setting. Railroads made that untenable. If a train heading from New York to Chicago was supposed to pull into a siding if it got to that siding before 11:45 AM to let the train from Chicago to New York go by, was that 11:45 Chicago time, New York time, or local time? After a few train accidents when engineers disagreed about time was meant to be, the railroads divided the world into time zones so that everyone could agree what time it was at that siding east of Toledo where one of the trains might have had to wait.
Mind you, New York is at about 74 degrees west, so the Sun is overhead at about 11:56 AM in a time zone centered around 75 degrees west. Chicago is at 87 degrees west; noon there is at about 11:48 AM if the time zone is centered around 90 degrees west — or 12:48 if the time zone is centered around 75 west. Toledo, at 83.5 degrees has a choice: 12:34 if centered around 75 degrees west or 11:34 if centered around 90 degrees west. Since Toledo is in the state of Ohio, most of which is east of Toledo, staying on the 75 degrees west zone makes sense if the whole state will stay in one time zone.
Does it matter what time the sun is “overhead”? Most adults are awake for about sixteen hours a day, and in most latitudes, the sun is over the horizon — it’s “daytime” — for less than sixteen hours a day on any day of the year. So, we might rise before sun-up, and most of us remain awake after sunset routinely. If we wake six hours before noon and stay awake ten hours after noon, does it matter whether that’s 6 AM to 10 PM, 7 AM to 11 PM, or 12 PM to 4 AM?
Things like business’s working hours, meeting times for communal events, and laws about what time bars close are relatively constant if noon is usually between 11:30 AM and 1:30 PM, but if the world ran on UTC, mandating at bars close at 2 AM would work great in Europe but not so well in eastern Asia, where 2 AM UTC is well after sun-up. Of course, things like bar closings aren’t set by international treaty; they’re set by countries or even provinces within countries. Few countries span 45 degrees of longitude, three hours variation in noon, and even fewer provinces do. On the other hand, should a family moving from Virginia to Oregon have to shift their daily schedules by three hours or just shift their clocks by three hours? Two young cousins arguing about who has the later bedtime have a simpler argument if clocks shift than if schedules shift. Maybe that’s as good a reason for having time zones and keeping “noon” around 12 PM.
What, then, do we do about “daylight savings time”? We shift our clocks so our whole schedule is an hour later in solar time. Noon becomes centered around 1 PM, and we have more sunlight after 12 PM — and less sunlight before 12 PM. Whatever amount of time lights aren’t lit after dark is probably offset by whatever amount of time before dawn the lights are on.
I like the convention that the “noon,” when the sun is “overhead,” is at 12 PM, give or take half an hour. Living my life by UTC when I live a quarter of the way around the world from Greenwich, England, would be weird. Maybe if I’d lived my whole life that way, I’d be used to it, but people throughout history have been governed by when the sun rises and sets where they are, not some place they’ve never heard of. Let’s retain twenty-four hour-wide time zones (or even forty-eight half-hour wide time zones?).
And for everyone’s sake, get ride of Daylight Savings Time. All it does is confuse people.