Long before written records were kept, people were concerned with the seasons, important in agriculture, and the sky, which permitted them to read off the passage of time. Everyone knows that the year is the time it takes the sun to complete its orbit about the earth. (Copernicus notwithstanding, mathematical readers will see nothing wrong with placing the origin of the coordinate system at the center of the earth.) Also, a month is supposed to be the time it takes the moon to go around the earth; at least, this was the case before the lengths of the months were laid down by law. But what about the week ? Theological explanations aside, it is the smallest period, longer than a day, that can be easily observed by looking at the sky: the time it takes the moon to pass from one phase to another, from new moon to half moon, from half moon to full moon, etc.
KeywordsMathematical Knowledge Number System Full Moon Small Period Repeated Impact
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