In former times, the day was divided into twenty-four hours, but they were not of equal length. During the day, an hour was one-twelfth of the time from sunrise to sunset; during the night, it was one-twelfth of the time from sunset to sunrise. So the daytime hours were all equal, and the nighttime hours were all equal, but the daytime hours were not equal to the nighttime hours, except on the equinoxes, or at the equator. In the summer, the day hours were longer and the night hours shorter, and in the winter, vice versa.
Some years ago I suggested, as part of the Perl Quiz of the Week, that people write a greektime program that printed out the time according to a clock that divided the hours in this way. You can, of course, spend a lot of time and effort downloading and installing CPAN astronomical modules to calculate the time of sunrise and sunset, and reading manuals and doing a whole lot of stuff. But if you are content with approximate times, you can use some delightful shortcuts.
First, let’s establish what the problem is. We’re going to take the conventional time labels (“12:35” and so forth) and adjust them so that half of them take up the time from sunrise to sunset and the other half go from sunset to sunrise. Some will be stretched, and some squeezed. 01:00 in this new system will no longer mean “3600 seconds after midnight”, but rather “exactly 7/12 of the way between sunset and sunrise”.
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