Daily Talk
To find where the moon actually is, the Rambam first measures how far it stands from the sun and then doubles that number. Everything downstream hangs on the result: how much to correct the moon's average path, how large the correction comes out, and whether you add it or take it away. Why should the true position of one body be a function of its distance from another?
The Doubled Distance
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About This Talk
Chapter 15 completes the reckoning of the moon by turning the mean positions into a true one. The Rambam subtracts the sun's mean from the moon's mean, doubles the remainder into the double elongation, states that this figure can never fall below five degrees or rise above sixty-two on the night of a sighting, and gives a table converting it into an addition of one to nine degrees that yields the correct course. He then supplies the angle of the course for every ten degrees, rules that the angle is subtracted from the moon's mean below 180 degrees and added above it, vanishes entirely at an even 180 or 360, and closes with a fully worked example for the night of the second of Iyar that lands the moon in the nineteenth degree of Taurus.