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Re: Negative numbers
From: Alexandre Eremenko
Date: 2024 Mar 9, 15:13 +0000

David, You wrote: > I imagine there's also the problem of different authorities assigning negative numbers to different directions. SHA increases to the west while right ascension (e.g. > 2102-D star finder) increases to the east. Avoiding negative numbers can help avoid headaches when using references from different publishers. There is a very fundamental reason for this. The whole celestial sphere (currying stars, planets, Sun and Moon with it) rotates clockwise (daily rotation), if you observe from the Northern hemisphere. That is E to W. That is the direction of increase of hour angle. This is why the hands of our watches rotate this way. With respect to this sphere, everything (planets, Sun, Moon) rotate counterclockwise (this comes from the yearly rotation of the Earth and planets around sun, and Moon around the Earth.) So they choose this as positive directions in all coordinate systems which do not depend on the daily rotation. These choices were made in antiquity, exactly with the purpose to minimize or avoid using negative numbers:-) Alex.

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