By Jerome Weatherald
BBC Radio Four
In Shifting Meridians on BBC Radio 4, the British explorer Benedict Allen has been uncovering the riddles of the world time zone map. Producer Jerome Weatherald found the history of time head-scratchingly mysterious.
Most of us know that France is an hour ahead of the UK, New York is five hours behind, and Australia - well, 10 or something hours ahead.
Millennium Island, Kiribati; first place to experience the year 2000
But in terms of global time, that kind of knowledge does not even scratch the surface of the complexities and curiosities of the different time zones around the world.
How about this for starters. China, that vast country that stretches across five hour zones on a globe, has only one time zone - Beijing time, to the east. Yet Russia has 11, and the USA six.
The UK shares a time zone with Portugal, the Canary Islands and the majority of western Africa - but not with France and Spain, both of which sit on the same Greenwich Meridian which is the basis for UK clocks, Greenwich Mean Time (GMT).
India reportedly snubbed its former rulers by choosing to be five and a half hours ahead of GMT ("turn your watch upside down if you're in the UK, and that's the time in India", the saying goes); and what is Nepal doing on GMT plus four and three-quarter hours?
Five years ago the explorer Benedict Allen embarked on a solo trek across the arctic wastes of eastern Russia with a team of dogs in an attempt to cross the Bering Strait to Alaska.
As the ice began to break up, he found himself adrift on a block of ice unintentionally going backwards and forwards across the International Date Line, not knowing whether it was today, tomorrow or yesterday.
Benedict Allen began pondering time zones while on floating ice
This got him thinking about how time, as well as geography, has come to define our place on the planet.
One look at a time zone map of the world reveals a globe carved up like a child's jigsaw. No two pieces are the same; there are no straight lines connecting the North and South Pole.
Some pieces are so small you can barely see them; others crash into each other in defiance of the beauty of the longitudinal lines that divide the world into 24 perfect segments.
So what lies behind this extraordinary document, and what does it reveal?
The International Meridian Conference of 1884 established Greenwich as the Prime Meridian, zero degrees longitude. But that proved to be the starting gun for a major re-organisation of the globe.
Countries were free to choose whatever time they wanted, regardless of the position of the Sun and its relationship to the clock on the wall.
Broadly organising themselves along the longitudes established by Greenwich, countries soon realised that time is power. For example, after initially opting for five time zones, in the Chinese Revolution of 1949 the authorities in Beijing symbolically adopted a single time zone dictating time across their vast country.
One effect of this was that on one side of the Afghanistan-China border it is GMT plus four and a half, while just over the border in China it is three and a half hours later (fancy starting work when the clock says 3am, anyone?)
The world time zone map is a living, ever-changing beast. The island nation of Kiribati on the equator used to straddle the International Date Line, meaning that half of its islands were a day ahead of the others.
In 1995 they decided to align themselves with the time in Asia, creating a finger on the International Date Line extending thousands of miles to the east into yesterday, as it were.
The squiggles and dog-legs in the South Pacific deserve a whole programme to themselves.
You would think there would be 24 time zones across the world. But at the last count there were 39.
"One of the most preposterous things that an alien would find coming from Mars and landing on Earth is that our time zones have no rhyme or reason," says professor of theoretical physics Michio Kaku.
"Any Martian would say how silly humans are that they can't even decide what time it is, which is one of the most basic aspects of being civilised."
You can listen to Shifting Meridians at Radio 4's Listen again page. The programme was broadcast on Sunday 21 May.