Dhanu (month) followed by the solar month of Makara. The Dhanus month is called "Margali" in the Tamil Hindu calendar. The ancient and medieval era Sanskrit texts of India vary in their calculations about the duration of Dhanus, just like they do with other months. For example, the "Surya Siddhanta" calculates the duration of Vrschika to be 29 days, 7 hours, 37 minutes and 36 seconds. In contrast, the "Arya Siddhanta" calculates the duration of the Vrschika month to be 29 days, 8 hours, 24 minutes and 48 seconds. Dhanu is also an astrological sign in Indian horoscope systems, corresponding to Sagittarius
Aryabhatiya to modern astronomy and mathematics. Aryabhata asserted that the Moon, planets, and asterisms shine by reflected sunlight, correctly explained the causes of eclipses of the Sun and the Moon, and calculated values for π and the length of the sidereal year that come very close to modern accepted values. His value for the length of the sidereal year at 365 days 6 hours 12 minutes 30 seconds is only 3 minutes 20 seconds longer than the modern scientific value of 365 days 6 hours 9 minutes 10 seconds. A close approximation to π is given as: "Add four to one