Explores the first Mitzvah in the Torah - Kiddush Hachodesh. Our main focus will be the concept of the number of days in each month (29 or 30) and how it affects the halachos of Rosh Chodesh (such as if one forgets to recite Yaaleh V'yavo). We discuss the different opinions amongst the Rishonim in the event that the witnesses do not arrive in time.

We will focus specifically on crystalizing why Rosh Chodesh is sometimes one day and sometimes two - and why our months are sometimes 29 days and sometimes 30 - and how this plays out in today's Halacha l'maaseh. In our introduction page, we provide clear and concise background to Kiddush HaChodesh in general, and how it evolved into our current calendar.