150 years BC, Hipparchus measures the length of a year with an accuracy of 6 minutes. He makes a list of the positions of the bright stars and after observing the unequal duration of the seasons, he states that the orbit of the sun around the earth is elliptical. (Geocentric model) #nasa #astronomy #astronomer #greek #hipparchus #length #year #geocentric #season #sun #earth #elliptical #star #mohammadhosseinsalimi_1 @nasa @EuropeanSpaceAgency