Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 3 · Name Letters and Chakras
युद्धजयार्णवः (चक्राणि)
चन्द्रो राहुस्तथाऽऽदित्य एकराशौ यदि स्थितः ।मुखग्रासस्तु विज्ञेयो जामित्रे पुच्छ उच्यते ॥ १८ ॥
In the full Agni Purana this is chapter 130, verse 18.
If the Moon, Rahu and the Sun stand in one sign, know it as a face eclipse. If one of them is in the 7th, it is called a tail eclipse.
Simple meaning: Sun, Moon and Rahu in one sign make a face eclipse. One in the 7th makes a tail eclipse.
भानोः पञ्चदशे ह्यृक्षे यदा चरति चन्द्रमाः ।
When the Moon is in the 15th nakshatra from the Sun and a moon day ends, foretell a Moon eclipse.
प्रदक्षिणमकारादीन्स्वरान्पूर्वादितो लिखेत् ।
Write the vowels round a circle from the east. The months start from Chaitra. Moon days are listed next.
त्रयोदशी चतुर्दशी अष्टम्येका च सप्तमी ।
These moon days are listed. Twelve moon days are counted from the first to the thirteenth.