Shloka 20
आत्मदर्शन-उपदेशः (Ātma-darśana Upadeśa) — Mind, Senses, and the All-pervading Self
चत्वार्याहु: सहस्राणि वर्षाणां तत्कृतं युगम् । तस्य तावच्छती संध्या संध्यांशक्ष तथाविध:
catvāry āhuḥ sahasrāṇi varṣāṇāṁ tatkṛtaṁ yugam | tasya tāvacchatī sandhyā sandhyāṁśaś ca tathāvidhaḥ ||
毗耶娑说道：智者宣称，克利多（Kṛta／萨提亚）劫为四千年。其黎明（sandhyā，交界）为四百年，其暮光之分（sandhyāṃśa）亦同此数。由此，经文确立了神圣的时间尺度，使诸劫得以依德行之盛衰而衡量、分等。
व्यास उवाच
Educational Q&A
The verse defines the traditional measure of the Kṛta/Satya Yuga: 4000 years proper, plus transitional periods—400 years of sandhyā (opening) and 400 years of sandhyāṃśa (closing)—highlighting that cosmic time is structured and that moral conditions are understood to vary by yuga.
In Śānti Parva’s instructional setting, Vyāsa is explaining yuga-structure and the lengths of the ages, giving a precise breakdown of the Kṛta (Satya) Yuga along with its junction-periods (sandhyā and sandhyāṃśa).