Almost everyone recognizes a cycle of seasons that repeats once a year. Usually that year is defined as 365 days, more or less, because that’s how long it takes for the sun to complete its cycle in the sky. However, Jews and Muslims consider the year to be based on the moon’s cycles, which means years of 354 or 383 days, more or less.
When does the year start? The oldest continuously-recorded living culture, the Assyrian, starts its year on the Spring Equinox, which for complex reasons they celebrate on April 1. In 2018 our time, April 1 is the first day of 6768 Assyrian time. Many other peoples start the year on the Spring Equinox, most notably the Persians (Iranians), who call it Newruz. They influenced the Parsis of India, the Uzbeks, Kazakhs & Uighurs of central Asia, the Kurds, the Baha’i, and others. All start on March 20 or 21. Here’s a Kurd Newroz
Pre-Christian Slavic cultures began their year in early March, while ancient Athens started in mid-summer.
The ancient Romans originally started their year on March 1, but changed it to January 1 around 200 BC. Old Norse and Germans also began the year Jan. 1.
For that matter when does the day start? To the Celts, it made sense to think of time as progressing from darkness to light. Thus their day started at dusk, and their year started on October 31.
The Jews also think of the day starting at dusk. Their months are more regular than most – 29 or 30 days, same as the moon. (The moon is actually 29¼ days). Since there are 12.4 lunar months in a solar year, Jewish years can have either 12 or 13 months over a 19-year cycle. 12 months except for years 3, 6, 8, 11, 14, 17 & 19. The year starts from Sep 5 – Oct 5.
The world of Islam also considers the day to start at dusk, and their calendar is also based on the lunar cycle, yielding a year of 354 days. Thus the first day of the Islamic year begins approximately 11 days earlier each Christian year. Year one is the year Muhammad emigrated from Mecca to Medina; the Christian year 622 AD. In 2015 the year began on October 14.