-: The Earth :-
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-: The Earth and its rotation :-
We use an earth-like planet. The various difficulties of four-dimensional
orbits shall be ignored, we suppose other magic brings to bear here.
The nature of rotations is that energy is equalised between the several modes,
so a uniformly dense planet will tend to settle to a uniformly equal clifford
rotation. All parts of the earth has a 24-hour day, divided into half of day
and half of night. We only get this on the equinoxes.
We suppose the ancient model is seen: the viewer imagines the land does not
move, but the sky is moving around it.
East and West
The common measure for stars against the earths rotation is angle of right ascession.
This supposes that the zenith pointer (an arrow, pointing straight upwards), is
actually the hour-hand of a siderial clock, and that the circle is thus measured in
hours and minutes. So if a star of known time 14:00 is directly overhead, that's the
siderial time.
The stars always rise in the same place, and set exactly opposite on the horizon.
The celestial vault is a half-glome, the horizon is a full sphere, dividing into an
East and West half. The line between the east and west half is the like of horizon
stars: stars which never rise nor set.
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