Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 5 · Portents, Comets
ग्रहचारः केतवश्च
एकोऽपि भिन्नरूपः स्याज्जंतुर्नाम शुभाय वै ।यावन्तो दिवसान्केतुर्दृश्यते विविधात्मकः ॥ ९५ ॥
In the full Narada Purana (Purva Bhaga) this is chapter 56, verse 95.
Even one comet may take different forms. One named Jantu is for good. (Our text is unclear here: the meaning of 'jantur nama'.) For as many days as a comet of many forms is seen,
Simple meaning: 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.
ह्रस्वः स्निग्धः सुप्रसन्नः श्वेतकेतुः सुवृष्टिकृत् ।
A short, bright white comet that soon fades brings good rain. A long one brings drought.
अनिष्टदो धूमकेतुः शक्रचापसमप्रभः ।
The smoke comet is bad and can bring harm to a kingdom.