For years we have taught that the original calendar of Yahweh consisted of 360 days (12 months of 30 days - a fact clearly seen within the numerical prophecies of Daniel & Revelation). A perfect circle of 360 degrees, mirrored as well in the other 'oth or signs of the covenant (the rainbow, and yes even circumcision). Yet due to several huge calendar shifts documented in the Torah, our current year is 365 days. Yet unbeknownst to us, that does not affect or hinder Yahweh's perfect 360 days Feast cycle and calendar system. Where other calendars highlight the role of the moon, Genesis 1 clearly states that the luminaries created for signs and for seasons (the calendar calculations) are the Sun and the lesser light - the stars or constellation signs. The beginning of the year based on the Torah's instructions commences at the Spring Equinox (when the straight line shadow is seen). The very next day is Aviv/Nisan 1 - the first day of the first month of the new year.
Yahweh's Calendar is then composed of 12 months of 30 days, and His feasts plug in accordingly.
Due to the changes regarding earth's rotation, we find ourselves left with approximately 5 extra days at the end of that perfect circle calendar cycle (yet those days are being shortened!). But instead of attempting to manipulate His perfect cycle (as all other calendars do with intercalation), these days are the days of waiting - where we wait on Yahweh (Isaiah 40:13) to see the straight line plowing and separating the new year from the old to begin again.
