1,255. Declaring a Leap Year

Hilchos Kiddush HaChodesh 3:18

We do intimidate witnesses whose testimonies are in dispute so that it will likely not be accepted and the month will be declared full. We do this so that their testimony will be upheld and the month sanctified in the proper time. Similarly, if witnesses come before the month is sanctified to contradict the testimony of the witnesses who saw the moon in its proper time, these witnesses are intimidated so that their testimony will not be accepted and the month will be sanctified in its proper time.

Hilchos Kiddush HaChodesh 4:1

A leap year is a year that has an extra month added to it. This extra month is always Adar, so a leap year contains two Adars: Adar I and Adar II. This extra month is added because Deuteronomy 16:1 says to “Safeguard the month of spring,” meaning that we should ensure that Passover always falls in the spring. If the extra month were not periodically added, Passover would occasionally fall in the summer or the winter.