To calculate the eccentricity and the longitude of the apogee of the orbit of the sun, Hipparchus used the intervals of the seasons. Consequently, he observed the tropics and the equinoxes by using several instruments. After him, Ptolemy followed the same way. In 16th Century, as it is known, the astronomers dwelt upon the dissatisfaction of this method because of the difficulty of the observation of the tropics. Are there any astronomers who took this problem up before 16th Century? We find the answer of this question in Al Qânun al Mas'ûdî of Birûnî. Birüni examines the sun in the sixth chapter of his book. He calculates the eccentricity and the longitude of the apogee of the orbit of the sun by using the old method.