Remember to put your clocks forward one hour this weekend as daylight saving time begins. But if you live in Spain then you are putting your clocks to the 'wrong time'.
The Prime Meridian of 0° longitude was fixed at Greenwich England in 1884. Greenwich was chosen because of the astronomical connections set down by the likes of Isaac Newton and Edmund Halley, that enabled sailors to use the moon to navigate and fix their longitude more accurately. The world's time is set from Greenwich, an imaginary line runs from the North Pole passing through Greenwich and continuing to the South Pole. All points to the east of this line are ahead while all points to the west are behind Greenwich Mean Time. Most of the Spanish peninsular is to the west of the meridian so the time should be either the same or one hour behind Greenwich time, yet it is one hour ahead of the UK time. This time difference was set by Franco in 1940, in order to be in line with Hitler and Germany, but recently there has been talk about converting back to the 'proper' time.
The first instruments for measuring time were sundials. Viewed from the northern hemisphere the sun tracks across the southern part of the sky from east to west, therefore its shadow travels around the sundial in a clockwise direction; this motion was continued when mechanical clocks were invented. If someone living in the southern hemisphere had invented sundials then our clocks would travel in an anticlockwise direction.
The Earth's rotation about its axis isn't constant and 12 noon is rarely the moment when the sun is at its highest in the sky so an average or mean time is given, this is where the Greenwich Mean Time (GMT) comes from. Because of the variations caused by the Earth's uneven rotation, atomic clocks are a far more accurate way of measuring time and leap seconds are added to bring everything back in line. Travelling at high speeds, especially space travel, can affect time. Einstein stated that local time would run more slowly at very high speeds. To test this theory an atomic clock was placed on board the Apollo rockets that travelled to the moon. On its return, the clock was found to be running out of sync with atomic clocks on Earth.
The International Space Station orbits the Earth every 90 minutes and so constantly crosses time zones. A set time was needed on board and so it was agreed to adopt Greenwich Mean Time as the standard time.