Varaahamihira

"There was indeed a time when the Sun’s southerly course began from the middle of the star Ashlesha and the northerly one from the commencement of the star Dhanishtha, as it has been so stated in ancient works. At present the southerly course of the Sun starts from the beginning of Cancer and the other from the initial point of sign Capricorn. The actual state of affairs which goes against the old statement can be verified by direct observation. The Sun’s change of course can be detected by marking everyday the position of a distant object either at sunrise or sunset, or by watching and marking the entry and exit of the shadow of the gnomon fixed at the centre of a big circle drawn on the ground."