Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 1 · Muhurta: Marriage, Home, Farming
ज्योतिःशास्त्रम्
रविचन्द्रौ समौ कृत्वा योगो भवति निश्चलः ।एकोना तिथिर्द्विगुणा सप्तभिन्नाकृतिर्द्विधा ॥ २३ ॥
In the full Agni Purana this is chapter 122, verse 23.
Add the Sun and Moon together. Then the yoga (Sun-Moon yoga of the almanac) is found. Take the tithi (moon day) less one and double it. Divide by seven. It comes in two forms.
Simple meaning: Adding the Sun and Moon gives the almanac's daily combination. The moon day, worked by seven, gives its half.
तिथिश्च द्विगुणैकोना कृताङ्गैः करणं निशि ।
A sum on the moon day gives the half for the night. Fixed halves fall at the month's end and start.
षष्ट्यब्दानां प्रवक्ष्यामि शुभाशुभमतः शृणु ।
In Prabhava there are sacrifice rites. In Vibhava people are happy.
शुक्ले च सर्वसस्यानि प्रमोदेन प्रमोदिताः ।
In Shukla crops are good. Pramoda brings joy. Prajapati brings growth. Angira adds to pleasures.