Why Rosh Hashanah is Celebrated for Two Days

The tradition of celebrating Rosh Hashanah for two days stems from an ancient method of determining the start of the Hebrew month based on lunar observation, rather than a fixed calendar. In the past, the Sanhedrin, the Jewish high court, would declare the new month after witnesses saw the new moon. This announcement, known as "Kiddush Hachodesh" (sanctification of the new month), was then relayed to communities across the land and abroad.

Because Rosh Hashanah falls on the first day of the Hebrew month of Tishrei, its exact date was particularly difficult to ascertain. When the month's start depended on lunar sightings, it wasn't always clear when the first day would be officially declared. Communities further away often received the news late, if at all.

To ensure the holiday was observed on the correct day, some communities adopted the practice of celebrating for two days. This custom guaranteed that even if news of the Sanhedrin's decision arrived late, the holiday would still be observed properly. This practice ensured that the holiday was observed on the correct day, even if the news of the month's sanctification arrived late.

Even after the establishment of a fixed Hebrew calendar, the two-day observance of Rosh Hashanah persisted. In Jewish law, the two days are considered a single, extended holiday period, referred to as "Yoma Arichta," meaning "one long day." Therefore, when people celebrate Rosh Hashanah over two consecutive days, they are upholding a custom rooted in a time before printed calendars, accurate timekeeping, or modern communication, when information relied on human testimony and its rapid transmission.