Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · War Astrology: Yogas, Nakshatras
युद्धजयार्णवः (योगाः नक्षत्राणि)
अश्विनी त्रिंशत्ताराश्च (रा च) तुरगस्याऽऽकृतिर्यथा ।यद्यत्र कुरुते वृष्टिमेकरात्रं प्रवर्षति ।यमभे तु यदा वृष्टिः पक्षमेकं तु वर्षति ॥ १९ ॥
In the full Agni Purana this is chapter 127, verse 19.
Ashvini has thirty stars. It looks like a horse. If it rains there, the rain lasts one night. When rain comes in Yama's star, it rains for a fortnight.
Simple meaning: Ashvini's rain lasts a night, Bharani's rain lasts a fortnight.
कोटचक्रं प्रवक्ष्यामि चतुरस्रं पुरं लिखेत् ।
Draw a square fort, with a square inside it, and another inside that.
नाडीत्रितयचिह्नाढ्यं मेषाद्याः पूर्वदिङ्मुखाः ।
The fort figure has three lines. Krittika goes in the east and Ashlesha in the south-east.
भरणी दक्षिणे देया विशाखां नैर्ऋते न्यसेत् ।
Bharani goes in the south, Vishakha south-west, Anuradha west and Shravana north-west.