Show Some Motions of the Earth Tho earth revolves on her axis in twenty three hours fiftysix minutes and four seconds sec-onds This time is required for one rotation from a star round to tho same star again The revolution is therefore called a sidereal day While the earth has been tunjing on her axis she has been advancing in her orbit and it will tako her four minutes on the aver ago to come in the same position in regard to the sun thus adding four minutes to the length of the sidereal day gives twentyfour hours for tho solar day Tho time of tho axial rotation has not varleti the hundredth part of a second in two thousand years It may therefore be considered as invariable and is consequently adopted as a fundamental funda-mental unit in astronomical measurement |