Question: What is the function of the sun in the Lunisolar calendar besides determining the start and end of a day?
Answer: In addition to determining the start/end of the day, the sun (in concert with moon) determines when a new year begins and ends. The Biblical year according to WLC’s studied conviction begins on the New Moon Day nearest the vernal equinox. (The vernal equinox is when the sun crosses the celestial equator in a northerly direction.)
For more on the Biblical Calendar, kindly refer to the following: