Astronomical Mentions in Other अङ्गः of Vedas कल्पः (Manual of Rituals) कल्पः has various सूत्र ( सूत्र is a large collection of such aphorisms in the form of a manual, it is a distinct type of literary composition, based on short aphoristic statements, generally using various technical terms. सूत्र forms a school of Vedic study). Types of कल्पः सूत्र are 1. श्रौता सूत्र has यज्ञ Rituals 2. गृह्या सूत्र - has Domestic Ceremonies 3. धर्म सूत्र -has -Religious and Social Laws 4. शुल्ब सूत्र -has Geometry and Mensuration सूत्र with some important astronomical mentions are अश्वलायन श्रौता सूत्र Names of months based on nakshatra and seasons are found in this text. The reference to seasons indicates that spring was considered the year's first season. Tithi is not mentioned specifically ,however use of words चतुर्दशी, अष्टमी indicate Tithis. Like in this verse...
The cosmos has a lot of hidden facts, and we are not aware of them. Humans have been learning from the heavens and updating their lives since ancient times. In doing so, we have forgotten the efforts of the previous generation who had opened the cosmos to us. Some facts we knew, but had no proof of, as we unfold and update, the facts confirm their findings. My effort is to bring out these fundamentals as given in ancient Hindu texts