about 13,000 years; or a complete revolution of the seasons back to where we are, in 26,000 years. Leaving out fractions to make the illustration plain, we have:-- (1) 360 degrees of Zodiac } --------------------- = 26,000 years } 50 seconds of arc } } (2) 1 day of time } ------------- = 26,000 years } 3-1/3 seconds } All } Approximate (3) 1 year of time } -------------- = 26,000 years } 20-1/3 minutes } } (4) 3-1/3 seconds } ------------- = 1/110 of a second} days in a year } In (1) we see that a "precession" of 50 seconds of arc will bring the Spring equinox around in 26,000 years. In (2) we see, as 50 seconds of arc represents the distance the earth will rotate in 3-1/3 seconds, a difference of one day will result in 26,000 years. That is since the clock regulated by the stars, or absolute rotations of the earth, would get behind 3-1/3 seconds per year, it would be behind a day in 26,000 years, as compared with a sidereal clock regulated by the Spring equinoctial point. In (3) we see that as 50 seconds of arc is traversed by the earth, in its annual revolution, in 20-1/3 minutes, a complete circle of the Zodiac will be made in 26,000 years.