Time for Time?
Question by Ethan Gelber

The Question:

On December 31 and January 1, the world watched the millennium counter click from 1 to 2 as a succession of midnights struck and launched a rolling wave of celebrations keyed into our modern time zone conventions. Beginning in Tonga, nestled into an eastward deviation of the International Date Line and thirteen hours ahead of Greenwich Mean Time, the clocks of the world began bonging the midnight hour. Twenty-four hours later, the celebrants of Midway and Phoenix Islands and Western and American Samoa, located at roughly the same longitude as Tonga but on the west side of the International Date Line, put an end to the millennium roll-over.

Who is responsible for our present-day system of dividing the world into 24 times?

What is the difference between Greenwich Mean Time, Universal Coordinated Time and Zulu Time?

Discounting islands, there are seven countries in the world that have adopted zones based on political boundaries (one time zone for the entire country) but whose times vary from the standard time zone by something other than an hour. What are these countries?

What time is it at the North and South Poles?

How fast do you have to travel west to arrive earlier than when you left?

The Answers:

Sir Sanford Fleming was first to propose dividing the world into 24 longitudinal 15-degrees-wide time zones, as we have them today. Born in Scotland but remembered today as one of the greatest of the 19th-century railway engineers in Canada, in 1863 Fleming was selected by the Canadian government to lead a survey of the eastern part (the first link) of what would grow to be the Canadian coast-to-coast Intercolonial Railway. In 1871, he was appointed engineer-in-chief of the planned Canadian Pacific Railway. He retired in 1880 and was knighted in 1897.

As early as 1878, Fleming had begun grappling with the inadequacies of the system of establishing local time. Long-distance railway travel in Canada and the U.S. had made clear the problems inherent in the old practice of setting clocks according to the sun. As an alternative, Fleming proposed a system whereby 24 time zones would account for hourly variations set against a standard, or mean, time. In 1884, he oversaw the International Prime Meridian Conference in Washington, D.C. The international system of standard time zones was agreed upon at that time.

Greenwich Mean Time (GMT), Universal Coordinated Time (UCT) and Zulu Time are all... you guessed it, exactly the same thing. It is the equivalent of zero degrees longitude and runs through the Royal Observatory at Greenwich in London, England.

Discounting small territories in the Pacific like Norfolk Island, Pitcairn Island, Chatham Island, and the Marquesas Islands, the following seven countries deviate from their standard geographical time zones by something other than an hour: Iran (3 hours and 30 minutes ahead of GMT), Afghanistan (4 hours and 30 minutes ahead of GMT), India and Sri Lanka (5 hours and 30 minutes ahead of GMT), Nepal (5 hours and 45 minutes ahead of GMT), Bhutan and Myanmar (Burma) (6 hours and 30 minutes ahead of GMT).

Grade-school geography taught us that longitude lines converge the closer and closer they get to the poles. In fact, at the North and South Poles, the lines all come to a point. Anyone living on or near the poles could walk a few steps and pass from one time zone to another. To avoid any confusion, anyone living in Antarctica and explorers venturing to the Arctic pole use the time in Greenwich, England.

The speed required to stay ahead of the changing time varies depending on the latitude of the traveler. For arguments sake, let's assume that our intrepid adventurer, Speedy, is on the equator at a point just to the west of the International Date Line. If he were to leave this point at precisely noon on any day, one question to ask is how fast would he have to travel, due west along the equator, to get to a point further west at a time earlier than when he departed.

Well, our GORP reference books tell us that the equatorial circumference of the earth is 24,901.45 miles. If we divide this into 24 parts (for the 24 15-degree longitudinal time zones) we learn that the theoretical distance between the western edges of each time zone is 1037.560417 miles. We know that it takes 24 hours for the earth to rotate once on its axis (or 23 hours, 56 minutes and 4 seconds for the picky). Thus, for Speedy to get from his spot just west of the International Date Line to a spot just west of eastern edge of the next time zone over at a time earlier than when he departed, he would have to travel faster than 1037.560417 miles every 59.8361 minutes, or basically 1040.4 mph. By the same token, if Speedy left his post at 12:10 a.m. and sped around the entire earth fast enough, he could return to a spot meters from where he began, but just to the east east of the International Date Line, at, say 12:09 a.m. of the same day.

This question becomes a little more difficult if Speedy were to change latitudes. There are two new problems: first, the rotation speed (in mph) is not the same as at the equator (i.e. the distance between the western edges of the time zones decreases; second, the shortest distance between the two points is not along the line of latitude, so Speedy would probably not fly along the line of latitude.

The first problem is easiest: just multiply by the cosine of the latitude. So for a city at 40 degrees latitude, the new distance between time zones is cos(40) or 0.766 times the true circumference of the earth. Thus the desired speed is 0.766 times the equator speed, or, in Speedy's case, 796.95 mph.

Now the second problem: The problem is that if Speedy were traveling between two cities not along the same latitude, he would probably try to fly along the shortest path between the two cities, and that shortest path is no longer along the line of latitude concerned. The shortest distance between two points on a sphere is along a"great circle" connecting the two points. A great circle is simply a true circumference of the sphere. The equator is a great circle, the other lines of latitude are not great circles. All of the lines of longitude are great circles. To find the speed faster than which Speedy would have to travel, you just need to find the distance between the two cities (click here to get the distance) along the "great circle" between hem and divide by the number of time zones that separate them. Note that as the latitudes of the two cities become more and more different, you have to fly faster and faster, and of course if the two cities are in the same time zone it is impossible.

Of course, for the picky, there are different degrees of error. For example, the earth is not a perfect sphere and there are winds to be taken into account. But even in a perfect world, Speedy would have to move fast.

GORP is indebted to Thomas J. Regan III, physics mind and numbers master, for his invaluable contribution to the answer to this particular question.

The Winners:

This was apparently a real toughie. So tough in fact that no one found the correct answer. It could be that the phrasing of the question wasn't as clear as it should have been. But it is probably also because this is about some pretty obscure stuff.

The four best  and very good!  answers came from Angelo Sciulli, S Jim, Matthew Bolz-Weber, and Linda Amadon, each of whom wins the coveted bag of GORP.com.

Angelo weighed in with two responses. His first was: "King Charles II of England in 1675 recognized the need to determine location and established the Royal Observatory to solve the problem. The culmination of that work was the adoption of the 24 time zones at the International Meridian Conference." His second guess was John Harrison, the 18th-century English clockmaker remembered today as the inventor of the first marine chronometer used for accurately calculating longitude while at sea. While these were great guesses, neither King Charles nor John Harrison was the vital link  the person  who tied the 24 hours of the day to 15-degree longitudinal swaths of the earth.

S Jim contributed the name Sir George Biddell Airy. Sir Airy was English astronomer royal  director of the Royal Greenwich Observatory  from 1835 to 1881. He certainly did a great many things during his lifetime, but was not the gray matter behind the first time zone epiphany.

Finally, Matthew and Linda both put forward Gerhardus Mercator, the 16th-century Flemish cartographer best remembered for innovative cartographic skills (ubiquitously employed today in "Mercator projection" maps). Maps using this kind of projection show longitudinal lines as evenly spaced straight parallels, which in fact they are not. Contemplation of maps drawn with a Mercator projection make it easy to understand the time zone system. However, Mercator is not recorded as ever having made the connection between meridians and time standards.

So, given that no one got the basic question right, does anyone win a GORP pullover? Yes, indeed! Angelo was the first to respond to all questions with answers that showed care and knowledge. On the extra-credit questions, he got the 1st and 3rd right. We have some differences regarding question 2, but they are negligible. And his answer to question 4 was amazing: "As soon as one crosses the international date line heading east (from Japan to US) the day changes to the previous one. The absolute velocity (of course) is dependant upon the distances being covered and is defined by the equation v=d/t, where v is the velocity, d is the distance being covered traveling from a to b and t is the time required to travel from a to b. Alternatively, the slowest velocity would be the time to return to the starting point. In a worst case scenario, consider starting at a point on the equator and returning to the same point and arriving earlier(the previous day). The maximum time to accomplish this would be equal to the circumference of the earth at the equator ~25,280 miles in (24 - x )hours (where x is a defined unit of time i.e., one second, one picosecond). r=25280 miles/24 hours - x hours. As x approaches 0, r = 1053 miles/hour. Alternatively, invoking Einstein's theory of relativity, as velocity approaches the velocity of light, time slows down. Theoretically, I suppose that if one exceeded the speed of light, one could back in time. In that case starting point and ending point would be irrelevant and the governing rate would be exceeding the speed of light (3x10exp8 m/s)."

S Jim seemed to agree: "If the question is to go back even 1 minute one would have to travel faster than the speed of light, which can't be done nor would you want to travel at that speed."

THANKS for your contributions!