Does anyone really know what time it is? What a mess the world's time zones are! China has only one time zone for the entire country, while the US (not including Hawaii and Alaska), which covers the same approximate east-west distance as China, has four time zones. In Russia, which has 11 time zones, the time in each zone has been advanced an hour from the time that would be appropriate for that zone.

To give you an idea how confusing it can be to try to figure out what time it really is in some places, the following description is for the Australian Territory of Lord Howe Island, about 440 miles northeast of Sydney. The time zone is 30 minutes ahead of Australian Eastern Standard Time (AEDT). Note that in summer, clocks are turned forward 30 minutes, so that time is the same as Sydney (AEDT). So standard time is GMT*+10:30, and daylight saving time (DST) is GMT*+11:00. Dates for DST cutover are the same as New South Wales (see above). However, this is not the case for 2000. Sydney is changing to DST in August for the Olympics. Lord Howe will change over to DST on 29 October 2000. Good grief! Howe must have made the mistake of asking "the Professor" to compute the time for the island - he should have asked Gilligan.

At the end of the 19th century, time zones were introduced using the Greenwich Meridian (0 degrees longitude) as the "agreed-to" prime meridian or starting point. Since there are almost exactly 24 hours in a day and 360 degrees in a circle, each time zone was set up to be 15 degrees in width. So, it takes the Sun approximately one hour to traverse each time zone. Thus, if the Sun is at its highest point in the sky over Berlin, Germany (15 degrees east longitude), it'll be at its highest over London (0 degrees longitude) one hour later. In theory, each time zone extends 71/2 degrees east and west of the 15, 30, 45, 60 ...meridians. This means that for no place within the 15 degree time zone will the clock time vary by more than 30 minutes from the Sun time. However, for historic, cultural and economic reasons, there are deviations from this rule.

For example, Madrid, Spain is in the same time zone as most all of Europe, except the United Kingdom and Portugal. The result is that even though Madrid is nearly 200 miles west of London, it's in the time zone to the east of London. So, when it's 8:00 a.m. in Berlin, it's also 8:00 a.m. in Madrid, but 7:00 a.m in London. As the Sun comes up over London, it's nearly pitch dark at 8 in the morning in Madrid.

To complicate things further, some countries observe daylight savings and some don't. Even here in the States, Arizona, Hawaii, and a good part of Indiana never change their clocks. Most of the rest of us will set our clocks back this coming weekend. In the US, we move from daylight savings time to standard time at 2 a.m. on the last Sunday of October. We set the clocks back an hour - we get an extra hour's sleep! Then in early April, clocks are advanced an hour. There really aren't any astronomical reasons for changing the clocks, it's done for political and social reasons.

The idea behind daylight savings time is to give us more daylight in the evenings when most of us can enjoy it. The tradeoff is that the Sun comes up an hour later than it would if we were on standard time. However, since the majority of us are still in the sack at 5:30 in the morning, we wouldn't notice if the Sun is up or not, and it's easier to sleep when the Sun is still below the horizon. Of course, it's no fun to wait at the school bus in the darkness, and farmers don't care to do their morning chores when the Sun hasn't even thought about coming up.

Because most of us crave sunlight, and we want to be awake when the Sun is up, cities near the eastern edge of time zones have often found a way to have the time zone relocated so that their city is in the more eastern zone. The point being that they'll have about an hour more light in the evening than if they were in the eastern portion of a time zone. For instance, Cincinnati is in the western part of the eastern time zone rather than in the eastern part of the central time zone. In fact, in each time zone in the US, far more people live west of the standard meridian that bisects the time zone than east of it; approximately 35% of the population lives east of the standard meridian while 65% live west of it. From 1918 to1977 there were 49 changes in the four time zone boundaries, and all but four of them involved a westward change or boundary migration.

But I've digressed from the original question about time zones that differ by only 1/2 hour or 90 minutes from adjacent time zones. When we visit other parts of the world, things get even stickier in regards to time. In New South Wales, Australia, for instance, clocks are turned back at the end of March (remember it's the Southern Hemisphere) and moved forward at the end of August! Queensland, the Northern Territories and Western Australia don't participate in daylight savings at all. So the time is an hour earlier in Sydney, New South Wales than it is in Brisbane, Queensland, which is just a little further north of Sydney. Since Australia has three conventional (east-west) time zones, it actually has both vertical and horizontal time zones! Additionally, Australia, as well as a handful of other countries including Iran, Afghanistan, India, Sri Lanka, and Myanmar (Burma), has time zones that differ by a half hour or 90 minutes from adjacent time zones.

Again, there are no astronomical conventions for these unusual time changes. They're made for practical reasons or what seemed to be practical reasons at the time they were implemented. For example, India spans almost exactly two time zones, but their government decided that they wanted one time for the entire country. Their solution was to split the difference between what the time would be if they used two zones. So, Instead of the time being 10:00 in Bombay and 11:00 in Calcutta, the time is 10:30 in both places. Iran covers only about one time zone width, but it's nearly bisected by the 45 degree (east) meridian, which means that their residents would be in two different time zones. Thus, the government of Iran also chose to split the difference.

Australia is the only country that has a time zone within its borders that differs by more or less than an hour from adjacent time zones. The three time zones in Australia don't split the individual states - uniformity of time is maintained within each state (Australia has 6 states and 1 territory). It was decided in 1898 that the standard meridian for the central time zone of Australia would be 142 degrees and 30 minutes east longitude rather than 135 degrees east longitude. This is only 7 1/2 degrees from the standard meridian for the eastern time zone of Australia (150 degrees east longitude). Because of this, a city such as Darwin (about 131 degrees east longitude) is nearly 12 degrees west of the standard meridian for the central time zone. It's still in the central time zone, but in actuality, since it lies more than 7 1/2 degrees from the standard meridian, it should be in a different time zone all together. Therefore, the standard time in Darwin is approximately 46 minutes in advance of the Sun's position in the sky, but there's just 30 minutes difference in time, instead of an hour, between the Northern Territory and Queensland, the state to its east. However, for someone going west from Darwin into Western Australia, there's a 90 minute time change!

If we do know what the time is, we probably don't understand why it's the time that it is.

For more about this see Scientific American, Standard and Daylight-saving Time by I. Bartky and E. Harrison and the science question for October 25, 1996.

27 October 2000