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
Surya Siddhanta in South and Southeast Asia are rooted in this text, but the regional calendars adapted and modified them over time. The "Surya Siddhanta" calculates the solar year to be 365 days 6 hours 12 minutes and 36.56 seconds. On average, according to the text, the lunar month equals 27 days 7 hours 39 minutes 12.63 seconds. It states that the lunar month varies over time, and this needs to be factored in for accurate time keeping. According to Whitney, the Surya Siddhanta calculations were tolerably accurate and achieved predictive usefulness. In Chapter 1 of "Surya Siddhanta", states Whitney, "the Hindu