jay@npois.UUCP (Anton Winteroak) (02/26/85)
It appears that Al-Zarqali determined the position of the sun at aphelion using his famous water clocks. He appears to have noted the time of solar noon, the shortest solar day is perihelion, the longest is aphelion. In the 26 years that he made these measurements, the time of perihelion changed by about 2 hours. I believe that he would have been able to measure that it was changing, but to acheive his accuracy, he must have also used an old greek value for the position, and used a longer time base. I've calculated that he would have been able to determine the date of perihelion to within three days, by direct measurement of the diameter of the sun. But this would not be enough accuracy. I believe you are right about aristarchus, and his measurement, but I understand that that was what tipped him off that there was a perihelion, and that he to measured itoo measured it more accurately with water clocks.