Dear Sundial Friends, The sunset behind an unobstructed horizon should be observed by three different observers on three different floors of a building. From the two distances of their eyes and the three times when the last sunrays fall into their eyes we then can calculate the acceleration of the terminator. On the west coast of Portugal at a geographical latitude j=40° we get quite comfortable values: 60s after sunset with solar declination d=10° the sun is 11 below the horizon and the terminator has reached a height of 34m above the ground with an acceleration of 1.876cm/s². According to my calculations the fudge factor is F=cos²d-sin²j=0.5567. With T=86400s we have R=aT²/4/p²/F=6372km. This is different from the inaccurate result R=2612km we get with the fudge factor F=cos²d+sin²j *(cos²d-tan²d)=1.3577 given in David Bowmans article. Regards, Rolf Wieland
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