Get out two balls and mark a spot on one of them as my location on the Earth, then revolved it around the second ball ( the Sun) while rotating the Earth ball exactly once. It is pretty obvious that in a 1:1 resonance, the Sun stands still in the sky so that you get a full year of daytime if you are on the hemisphere facing the Sun, and a full year of nighttime if you are on the opposite side of the Earth. This situation will persist indefinitely. The only way you would get 1/2 year of day/night is if the Earth remained pointed to the same point in the sky which would happen if the rotation velocity of the Earth went exactly to zero. This situation is not very plausible on a dynamical basis. From the Earth, you would be able to point your telescope at any star in the sky, and over the course of a full year, its position in the eyepiece would remain perfectly fixed. For the 1:1 resonance, the star would drift by 1 degree per 'day' rather than its current diurnal rate which is 15 degrees per hour.
Copyright 1997 Dr. Sten Odenwald
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