They observed the state of the crops, considered the need to make the Passover journey by way of muddy roads and tried to insert the leap month in an advantageous way.In 432 BC the Athenian astronomer Meton reformed the Athenian calendar based on an approximate relationship between the solar and lunar cycles.The Jewish calendar, on the other hand, maintains both the lunar and solar relationship and also adjusts for certain religious requirements.The establishment of such a calendar was a remarkable accomplishment for a people living more than 2,000 years ago.Of course, a practical calendar must have a whole number of days in each month.Since the lunar month is very nearly 29 1/2 days, a calendar that has twelve months alternating between 29 and 30 days (averaging 29 1/2) would essentially follow the lunar cycle.During the period of the Second Temple (built between 519 and 516 BC.) and for three centuries after its destruction, a council of the Sanhedrin (the governing body of the time) decreed when the new months would begin and when adjustment was needed to compensate for the seasonal shifts.The start of each month was established by observing the arrival of the new moon.
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Once the council had made their declaration the new month was announced by means of fire signals to inform the communities outside of Jerusalem.By the end of the period of the Second Temple the months had again received new names that are used today.The names are Babylonian and were probably adopted shortly after the Babylonian Exile.But, unfortunately, the solar year and the lunar cycles are not synchronized.
While the present calendar (Gregorian) had its roots in the lunar cycle as evidenced by the length of the months and even the word "month" itself, it was adjusted to the solar year in order to maintain the seasonal references - its relation to the lunar phases was eventually abandoned.
So if seven lunar months were added over a nineteen year period the lunar and solar cycles could be more or less maintained in synchronization.