अयने चाहनी प्राहुर् वत्सरो द्वादश स्मृतः ।
संवत्सरशतं नॄणां परमायुर्निरूपितम् ॥ १२ ॥
ayane-in the solar movement (of six months); ca-and; ahani-a day of the demigods; prahuh-it is said; vatsarah-one calendar year; dvadasa-twelve months; smrtah-is so called; samvatsara-satam-one hundred years; nrnam-of human beings; parama-ayuh-duration of life; nirupitam-is estimated.
Two solar movements make one day and night of the demigods, and that combination of day and night is one complete calendar year for the human being. The human being has a duration of life of one hundred years.