It being the time of the new moon, Shatakratu saw in that Rudra (fearful) moment that the celestials and the Asuras were fighting on the Udaya mountain.
अमावास्यां प्रवृत्तायां मुहूर्ते रौद्र एव तु। देवासुरं च संग्रामं सोऽपश्यदुदये गिरौ॥