What time is it?
A seemingly easy question.
But at any given moment, the time will be different in different places in the world.
While one person is waking up to breakfast at 7am, another will be heading off to bed at 10pm.
Local time all depends on what time zone you're in.
A time zone is simply a region on Earth where the same standard time is used.
Time zones are based on longitudinal lines called meridians, which run vertically from the North to the South Pole.
If you were to split the Earth into 24 equal time zones, each 15 degrees apart, a time difference of one hour per zone would occur with the rotation of the Earth.
If it is, say, 2pm at one meridian, 30 degrees west will be two time zones, or two hours, behind – so here it would be high noon.
Between the first and last time zones lies the International Date Line, where you cross from one day to the next.
But who decided what time it was, and where?
Greenwich Mean Time
Whatever time it is now, it is the result of an historic event in 1884.
Sir Sandford Fleming, Inventor
At the International Meridian Conference, Canadian Sir Sandford Fleming proposed that time should be measured from Greenwich, London – a major trade and shipping hub.
The time used at this meridian was known as Greenwich Mean Time.
Using this as the agreed universal meridian, 24 time zones were established.
By 1929, most countries had aligned their clocks accordingly.
Because your body clock is adapted to the time zone you live in, moving around the globe into other time zones can affect you.
If you travel from London to Los Angeles, for example, you'll be eight hours behind the time that your body is used to.
This means you'll be hungry when you should be sleeping, and nodding off when it's time to go out and explore.
The time on your watch was set over a century ago.
But wherever you go, it will be constantly changing.