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1

Just a little calculations on the acceleration for a solar Sail: The impulse p of a photon of frequency ν, thus of energy hν , thus of wavelength λ = c/ν on the sail is p = hν/c = h/λ where h is Planck's constant (6.6 10^-34 Joules). To simplify the calculations, assume that the sun does not emit a whole rainbow of colors, but only the yellow-green color (λ =...


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No, in general, they don't close. (Though, as you say, some geodesics do.) Consider, for example, an oblate ellipsoid of revolution, and take two points on its equator such that the angle $\alpha$ between them is not a rational multiple of $\pi$. On a sphere, the only geodesic passing through tho points on the equator is the equator; but in our case, since ...


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