Then there's the thing about planting crops under a full moon to help them grow. Some modern gardeners swear by that.
Is it a coincidence that Easter is celebrated on the first Sunday after the first full moon after the vernal equinox? The pagan fertility festival that our modern Easter replaced was probablty on the day of the first full moon after the vernal equinox and so seems to point at planting crops at this time. If so then knowing when the equinox occured was rather important.