Brihat Samhita
पश्चात्सन्ध्याकाले संवर्तो नाम धूम्रताम्रशिखः । आक्रम्य वियत्त्र्यंशं शूलाग्रावस्थितो रौद्रः ॥ ११-५१ ॥
Samvarta Ketu is a comet which appears in the west in the evening with a tail of the colour of smoke and copper, extending to a third of the sky and resembling the sharp end of a dagger; it is fearful to look at.
english translation
pazcAtsandhyAkAle saMvarto nAma dhUmratAmrazikhaH । Akramya viyattryaMzaM zUlAgrAvasthito raudraH ॥ 11-51 ॥
hk transliteration by Sanscript