was based on the sun. I.e - the sun was at its highest point at 12 noon. This is known

as solar time.

And this worked fine when the best means of transportation was... somewhat limited...

but the advancement of technology made this problematic.

The United Kingdom was the first country to adopt a standard time zone, by using the mean

solar time at the Royal Observatory in Greenwich, England, which was known as Greenwich Mean Time.

The United States soon followed, by adopting 4 different time zones. The US also based

their time zones from the Royal Observatory, and were 5, 6, 7, and 8 hours behind.

Then, in 1884, an international conference between 26 nations decided that the Royal

Observatory in Greenwich would be used as the Prime Meridian of the world, marking zero

degrees longitude.

So because there's 24 hours in a day, 24 lines of longitude, every 15 degrees, mark the centre

of each time zone.

Although it's actually 25 time zones, -12 to +12 and including 0. Therefore, -12 and

+12 are half the size of all other time zones.

Today, every country in the world has one or more time zones, and use Coordinated Universal

Time, or UTC, which is an offset of the Prime Meridian.

But these lines of lonitude only mark the out ideal time zones, but every country can

chose its own time zones and is under no obligation to follow which time zone it actually falls into.

Because of this, there are several strange or complex time zones throughout the world.

Take China, for example. The 3rd largest country in the world, which should ideally have 5

time zones. But, it doesn't.

The whole of China uses the same time zone: Beijing Time, which is UTC+8.

This causes an unfortunate situation for people living in Western China, which should ideally

be using UTC+5 or 6, because sunrise can be as late as 10:17am, and solar noon can be

as late in the day as 3:10pm.

Because of this, people living in Western China either unofficially use UTC+6, or use

Beijing Time but adjust their day accordingly, by working from 11 to 7 instead of 9 to 5,

for example.

This big difference between official time and solar time in Western China means that

crossing the border to Afghanistan would result in a clock change of 3 and a half hours, because

Afghanistan use UTC+4:30. This is the biggest time zone change by crossing an international border.

Now, you may be surprised by Afghanistan's time zones... +4:30. I was surprised to learn

that not all countries' time zones are to the nearest hour. While the vast majority

are, there are six countries that use a standard time zone to the nearest half hour: Venezuela,

Iran, Afghanistan, India, Sri Lanka, and Burma.

Then there's also Newfoundland, Canada, as well as part of French Polynesia.

And then there's Australia... the absolute mother of half hour time zones.

Australia has 8 official time zones, and 4 of them are an offset to the nearest half hour.

Now, mainland Australia has only 3 time zones. The west coast uses +8 while the east coast

uses +10, so you can probably guess what the middle time zone is... nope. It's UTC+9:30.

The other 3 half hour time zones are on their outlying islands.

But if you thought half hour time zones were weird... it get even weirder, because there's

one country that use a time zone to the nearest quarter hour! Too cool for a regular time

zone or a quadrilateral flag... it's Nepal, which uses a time zone of UTC+5:45.

Although it's not the only place in the world to use a time zone offset by 45 minutes from

the hour. The Chatham Islands of New Zealand use +12:45, while the main islands use +12.

There's also one unofficial time zone at the very east of Western Australia, +8:45... which

is only used by about 200 people.

But there's one more reason why Australia is awkward when it comes to time zones: Daylight

Saving Time. See, while parts of Australia do use DST, other parts do not.

So those 3 mainland time zones in the winter, become 5 time zones in the summer.

Also, there's Lord Howe Island, which uses +10:30, and does observe DST, but only advances

its clocks by half an hour, using +11 in the summer. This makes Lord Howe Island the only

place in the world not to advance by a whole hour during Daylight Saving Time.

But by far the weirdest place when it comes to time zones is the international date line.

Now, in a perfect world, the line would be at 180 degrees longitude. Exactly opposite

the Prime Meridian.

But since all countries can choose their own time zones, the internatinal date line is

far from a straight line.

While you would expect time zones to range from -12 to +12, the furthest advanced time

zone is actually +14, which is unique to the Line Islands of Kiribati, which are about

the same longitude as Hawaii. Both are at the exact same time, but Hawaii is an entire

calender day behind.

Taking a closer look at the international date line shows just how complex the time

zones are.

The Line Islands are 26 hours ahead of the uninhabited US territory Baker Island, about

2000 kilometres west of the Line Islands.

Although, UTC-12 is an unofficial time zone, and all islands within this time zone are

uninhabited. The furthest behind time zone actually in use, is UTC-11, used by the country

of Niue, as well as several American terrirories.

This 25 hour time difference between Kiribati and Niue, means that every day, briefly, there

are 3 calender days in use at the same time.

At 10:30 AM on Wednesday in the UK, it's 11:30 PM on Tuesday in Niue, and 12:30 AM on Thursday

on the Line Islands of Kiribati.

But the international date line wasn't always like this...

Kiribati is made up of 3 islands groups: the Gilbert Islands, the Phoenix Islands, and

the Line Islands.

The Gilbert Islands were a British colony, while the Phoenix and Line Islands were part

of the United States. Then, in 1979, Kiribati gained independence from the UK, and the US

relinquished all claims to the Phoenix and Line Islands, which became part of the Republic

of Kiribati.

The time zones were: +12, -11 and -10. This became problematic, because offices on different

sides of the international date line could only conduct business with each other 4 days

a week, when both sides of the date line were on a week day.

So in 1995, their time zones were changed by shifting the eartern islands to +13 and

+14, drastically changing the shape of the international date line.

This also made Kiribati the first country in the world to enter the new milenium.

However, this wasn't the most recent change to the international date line. The most recent

change was in 2011, with Samoa switching sides.

Originally, the Samoan Islands were west of the international date line, but in 1892,

the Samoan king was convinced by American traders to switch to the east of the international

date line, to -11, just 3 hours behind California. The king agreed, in order to improve trade

with the United States, and the switch was made by repeating the 4th of July 1892.

Then, after more a hundred years, in 2011, the now independent country of Samoa, comprised

of the Western Samoan islands, switched back to west of the international date line, while

the eastern Samoan islands, American Samoa, stayed at -11.

This is because Samoa's biggest trading parters are now Australia and New Zealand.

So despite only being about 70 kilometres between Samoa and American, there's a 24 hour

time difference. 25 in summer, since Samoa follows Daylight Saving Time while American

Samoa doesn't.

The New Zealand territory of Tokelau followed and also switched sides at the same time.

And finally, one slightly odd country when it comes to time zones is Russia. Russia has

9 different time zones, yet they all seem to be... in the wrong place...

This is because Russia used to have 11 time zones, but switched to 9 in 2010. And then

in the summer of 2011, Russia advanced their clocks forward for Daylight Saving Time...

and just decided not to switch back again.

Since Russia is so far north, permanent DST gives Russia more sunlight during the evenings.

So with all the complications time zones cause, you think to yourself - do we even need time

zones? Couldn't the whole world just use the same universal time? Well... I used to think

that, and it may sound like a good idea in theory, but in reality it's not as practical

as you might think. But that's a topic for another time...

Thanks for watching.