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CalendarHome.com - Hour - Calendar Encyclopedia |
 | | The hour was originally defined in ancient civilisations (including those of Egypt, Sumeria, India and China) as either one twelfth of the time between sunrise and sunset or one twenty-fourth of a full day. |
 | | As a consequence, hours on summer days were longer than on winter days, their length varying with latitude and even, to a small extent, with the local weather (since it affects the atmosphere's index of refraction). |
 | | When, in post-classical times, a clock showed these hours its period had to be changed every morning and evening (for example by changing the length of its pendulum), or it had to keep to the position of the Sun on the ecliptic (see Prague Astronomical Clock). |
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