The Law Code of Yājñavalkya 1.10.6

1.10.6

yatra dine candramā na dṛsyate sā amāvāsyā, tasyām ahardvayavyāpinyām aparāhṇavyāpinī grāhyā, aparāhṇaḥ pitṝṇām iti vacanāt | aparāhṇaś ca pañcadhāvibhakte dine caturtho bhāgas trimuhūrtaḥ | aṣṭakāś catasraḥ hemantaśiśirayoś caturṇām aparapakṣāṇām aṣṭamīṣv aṣṭakāḥ ity āśvalāyanoktāḥ (ĀśGṛ 2.4.1) | vṛddhiḥ putrajanmādiḥ | kṛṣṇapakṣo 'parapakṣaḥ | ayanadvayaṃ dakṣiṇottarasaṃjñakam | dravyaṃ kṛsaramāṣādikam | brāhmaṇasaṃpattir vakṣyamāṇā | viṣuvaddvayaṃ meṣatulayoḥ sūryagamanam | sūryasaṃkrama ādityasya rāśeḥ rāśyantaragamanam | ayanaviṣuvatoḥ saṃkrāntitve siddhe 'pi pṛthagupādānaṃ phalātiśayapratipādanārtham | vyatīpāto yogaviśeṣaḥ | gajacchāyā,

The day on which the moon is not seen is the new moon (amāvāsyā); when it spans two days, that which spans the afternoon should be taken, because of the text, "the afternoon belongs to the ancestors." And the afternoon is the fourth part of the day divided into five parts, comprising three muhūrtas. The four aṣṭakās are on the eighth days of the four dark fortnights of the cold and dewy seasons, as stated by Āśvalāyana (ĀśGṛ 2.4.1). "Increase" (vṛddhiḥ) means the birth of a son and the like. "Dark fortnight" (kṛṣṇapakṣaḥ) means the waning fortnight. "The two solstices" are named the southern and northern. "Material" means rice-and-sesame porridge, black gram, and the like. "The acquisition of Brahmins" will be explained. "The two equinoxes" means the entry of the sun into Aries and Libra. "The sun's passage" means the movement of the sun from one zodiac sign to another. Although the solstices and equinoxes are established as being transitions (saṃkrānti), their separate mention is for demonstrating their superior fruit. "Vyatīpāta" is a particular astrological combination. "Elephant's shadow" (gajacchāyā) is defined as: