the history of time leofranc holford strevens oxford university press p has the following rule a th month is added under current rules in years and of a metonic cycle nine years behind the western 'golden number' cycle the month repeated which must not be a winter month or is that throughout which the sun will remain within the same sign of the zodiac subject to the rule that the equinoxes and solstices must fall in months and if this would be breached intercalation is postponed till after the second month of the following year i have not found holford strevens to be a particularly reliable source