Babylonian Calendar 360 Days. Since the 360 day hebrew calendar should be used when calculating the 70 weeks, if we calculated from 457 bc we would end up in 18 ad before the ministry of christ. They designated a circle to have 360 degrees to match their calendar, which had 12 months of 30.
That the ancient babylonian year had only 360 days was known before the cuneiform script was deciphered : 21, 2012, corresponds to day 21.25 of 360 calendar, which is six hours into the 21st day of the 10th or 11th month, and is teveth 8th on.