Daily Talk
The head and the tail are the two points where the moon's orbit crosses the sun's. Nothing occupies them. They are not stars, not planets, not anything a person standing in a field could ever be shown. The Rambam gives them a rate of travel, a table, a starting position on a particular Thursday night, and a location in the constellation of Virgo. Why does a system built entirely for the sake of an eyewitness spend a chapter tracking something no witness can see?
The Body That Is Not There
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About This Talk
Chapter 16 turns from where the moon is to how far off the sun's plane it is running. The Rambam defines the two crossing points of the tilted orbits as the head and the tail, gives the head a uniform motion in opposition to the order of the constellations at three minutes and eleven seconds a day, supplies its mean travel over ten, a hundred, a thousand and ten thousand days, and instructs that the accumulated mean be subtracted from 360 to yield the head's actual position, with the tail always exactly opposite. He then names the moon's inclination its latitude, fixes its absolute ceiling at five degrees north or south, and defines the course of the latitude as the true moon less the head, northerly below 180 degrees and southerly above it. A table of angles running to ninety degrees, an interpolation rule for units, and three reduction rules covering the rest of the circle complete the method, which he demonstrates on the night of the second of Iyar to yield a latitude of three degrees and fifty three minutes, southerly.