Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 5 · Portents, Comets
ग्रहचारः केतवश्च
दिव्यांतरिक्षा भौमास्ते शुभाशुभफलप्रदाः ।यज्ञध्वजास्त्रभवनरक्षवृद्धिंगजोपमाः ॥ ९३ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 93.
They are heavenly, of the mid-sky and of the earth, and give good and bad results. Some look like a sacrifice, a banner, a weapon, a house, a bear, a tree or an elephant.
Simple meaning: Comets are of the heavens, the mid-sky or the earth, and give good or bad results.
स्तम्भशूलांकुशाकारा आंतरिक्षाः प्रकीर्तिताः ।
Comets in the stars are heavenly, those shaped like objects are of the mid-sky, those on the ground earthly.
एकोऽपि भिन्नरूपः स्याज्जंतुर्नाम शुभाय वै ।
A comet can take different forms. How long it is seen sets how long its result lasts.
तावन्मासैः फलं यच्छत्यष्टौ सारव्यवत्सरैः ।
A comet seen for some days gives results for that many months.