Month and Year
the Year is not an exact number of solar days long
(shorter than 365 1/4 by 11m 14s)
we
have leap years to cover the 1/4 day (otherwise the seasons will slip)
we have more rules to cover the rest (no leap year every fourth century, etc.)
the rotation of the Earth is slowing down, so need leap seconds too
we have more rules to cover the rest (no leap year every fourth century, etc.)
the rotation of the Earth is slowing down, so need leap seconds too
the Moon does not go
around its cycle in an exact number of days (synodic period = 29.5 days)
months
(from moon) vary between 30,31 days (use Feb. to fix year)
lunar months will drift through the year (need extra month every so often if usually 12)
lunar weeks will have drifting weekends (religious out of phase with civil calendar)
lunar months will drift through the year (need extra month every so often if usually 12)
lunar weeks will have drifting weekends (religious out of phase with civil calendar)