What Are They & Why Do We Need Them?
We measure the day by saying that the sun is at it's highest point at 12 o'clock, midday. Because the earth spins, as it travels around the sun, one half of the earth is in darkness and one half in light, all the time. This brings us to a problem. If it is midday where you are, on the opposite side of the earth, it is dark, so what time is it on the opposite side of the world?
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