Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 3 · Name Letters and Chakras
युद्धजयार्णवः (चक्राणि)
ऐशान्यां च तृतीयादौ सप्तम्यादौ च याम्यके ।एवं कृष्णे सिते पक्षे वायौ राहुश्च हन्त्यरीन् ॥ १६ ॥
In the full Agni Purana this is chapter 142, verse 16.
On the 3rd tithi (moon day) and the ones after, he is in the north-east. On the 7th and after, he is in the south. So it goes in the dark and the bright half. Rahu in the north-west kills the enemies.
Simple meaning: Rahu sits in different directions on different moon days. In the north-west he kills enemies.
विष्टिराहुं प्रवक्ष्यामि अष्टौ रेखास्तु पातयेत् ।
Vishti Rahu uses eight lines moving round the directions from the north-east to the south, north-west, east and west.
नैर्ऋताच्च नयेच्चन्द्रं चन्द्रादग्निं ततो जले ।
Rahu with Vishti goes round the directions from the south-west through the north and south-east to the west and north-east.
इन्द्रादीन्भैरवादींश्च ब्रह्माण्यादीन्ग्रहादिकान् ।
Groups of eight, led by Indra, Bhairava, Brahmani and the planets, go round from the east. Vatayogini starts from the south.