Interesting point! about 366.2425ish, that never occurred to me. In principle is the same reason that when you roll one quarter once around another, the rolling quarter rotates twice, not once. --Dan
On Apr 8, 2015, at 5:08 AM, dupre@math.rutgers.edu wrote:
I noticed in the Scientific American article linked to in item 4 of vol 146 #18, the common error was made of saying that the length of the earth day was the time it took the earth to rotate once on its axis.
If the earth kept the same face to the sun, it would still rotate once on its axis in a year. Thus the earth rotates 366.2425 times on its axis in a year.
The length of a day could be defined by drawing a ray from the center of the earth through the center of the sun. Think of this ray as being affixed to the earth. As the earth rotates around its axis, in about 24 hours, this ray will come closest to the center of the sun again. This is one day.
Through how many degrees does the earth rotate on its axis in a day? (365.2425)/(366.2425) times 360 = 359.02 degrees in a day.