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प्रजापतिर्वै स्वां दुहितरमभ्यध्यायद्दिवमित्यन्य आहुरुषसमित्यन्ये तामृश्यो भूत्वा रोहितं भूतामभ्यैत् ... तमभ्यायत्याविध्यत्स विद्ध ऊर्ध्व उदप्रपतत्तमेतं मृग इत्याचक्षते य उ एव मृगव्याधः स उ एव स या रोहित्सा रोहिणी यो एवेषुस्त्रिकाण्डा सो एवेषुस्त्रिकाण्डा।
Prajapati felt love towards his own daughter, the sky some say, Usas others. Having become a stag he approached her in the form of a deer. ... Having aimed at him he pierced him; being pierced he flew upwards; him they call 'the deer'. The piercer of the deer is he of that name. The female deer is Rohini; the three-pointed arrow is the three-pointed arrow. — A.B. Keith, Rigveda Brahmanas, HOS 25 (1920), pp. 185-186
The Prajapati-Rudra myth read astronomically: Prajapati, become a deer pursuing his daughter (Rohiṇī, the red doe = Aldebaran), is pierced and 'they call him the deer (mṛga)' in the sky. The astronomical reading (Orion) is standard scholarship since Weber; Keith's own footnote records that 'the astronomical data here given afford Tilak the source of his work Orion.' The text names the asterisms but not the modern stars, hence 'likely'. Cf. ŚB 2.1.2.8-9 where Mṛgaśīrṣa is the pierced Prajapati's head/body.
Aitareya Brāhmaṇa 3.33 · text · translation