How many time zones does the world have?

sequoianoir

24 Oct 19 03, 4:44 PM

Gnomon

There are at least 31 time zones. They range from 12 hours behind GMT (Kiribati) to 13 hours ahead (Tonga), which makes 26 zones. In addition there are some zones which are half an hour displaced from the ones beside them: Marquesas Islands (-9.5), Newfoundland (-3.5), India (+5.5), Burma (+6.5) and Norfolk Islands (+11.5). There may be a few others I can't see on my timezone map. Oct 20 03, 2:34 AM

sequoianoir

Not sure how many (if any) of the "extra" ones are truly internationally recognised as genuine time zones. Since the introduction of GMT and the line of zero longitude, the French disputed that it should run through London (and time be determined from there) insisting that it should be Paris instead. This being the case, the French had their own time zone PMT, Paris Mean Time, differing by about 2 degrees longitude and 9 minutes 22 seconds from Greenwich and GMT. This meant it was still in time with the rest of the world but that GMT was really 9m22s behind the true meridian. This was still "upheld" by the French even after International agreement in 1884 (and they had been arguing for about 100 years) that GMT be the zero meridian and recognised as THE CENTRE OF TIME. The French kept this insistance (and their "own" time zone) right up until the late 1970's, where upon they recognised GMT "for the first time". HOWEVER, things are afoot YET AGAIN. The French are to resurrect PMT (unfortunate acronym) yet again. "LE MERIDIEN" is to be marked with trees and olive groves running nearly 1000 km through France joining 337 towns together. http://news.bbc.co.uk/1/hi/sci/tech/380035.stm Oct 20 03, 6:59 AM

gmackematix

I almost made the same comment as Gnomon but then thought that all the variations in the world's local time surely can't count as separate time zones. India seems to be the largest anomaly to the usual zones. Oct 20 03, 7:08 AM

Gnomon

One billion people use the +5.5 time zone in India. That should be enough to make it an internationally recognised zone! Oct 20 03, 7:09 AM

sequoianoir

But that is India being "lazy". The country falls into 2 time zones and instead of having half the country at +5 and the other half at +6, they have elected to set all clocks to 5.5 This does not exactly create a "new" time zone. Those people on the very east coast get up in "daylight", on the west coast it is still dark. Those in the east "go to bed" when it gets dark, in the west it is still "light". I believe that this is a fairly recent development and in the days of the British Empire, India had the "genuine" 2 time zones. In the mid 1800's hundreds of different times were adopted, each one corresponding to its own meridian. To simplify this situation, the Earth surface was divided into 24 adjacent, equal and equatorially perpendicular wedges, called time zones, each one delimited by two meridian forming a hour angle of 1 hour at the poles. The mean solar time of the central meridian of each time zone was assigned by convention to all places belonging to the time zone. The Greenwich time zone, centered on the homonymous meridian, was taken as reference time zone. In this way, the time zone right eastward Greenwich is 1 hour in advance in comparison with universal time (UT +01:00), while the time zone right westward Greenwich is 1 hour late (UT -01:00) and so on for all the others. The time zones division was officially adopted on 1884 November 1 at the International Meridian Conference held at Washington D.C. The figure shows the time zones division of the world. For political and administrative reasons, often the time zones are delimited by state borders instead of meridians. Some countries adopt a time different from their time zone. http://toi.iriti.cnr.it/uk/timezone.html#TIMEZONE Oct 20 03, 7:40 AM

Stew54

Odd factlet that amused me: When arriving in India from the UK, as a result of the +5.5 time difference there is no need to change your (analogue) watch. It will still tell the correct time if you just put it on upside down. Oct 20 03, 9:13 AM

Senior Moments

37 according to the map on http://aa.usno.navy.mil/graphics/TimeZoneMap2003.pdf Oct 20 03, 6:22 PM

robraw

There are about 39 time zones instead of 24 (as popularly believed). This is due to fractional hour offsets and zones with offsets larger than 12 hours near the International Date Line. http://en.wikipedia.org/wiki/Time_zone Aug 23 07, 7:08 PM