The Jewish calendar that has been in existence nearly 6,000 years never fails because it is based on the rotation of the sun, moon, and earth. Therefore, the date of any holiday can be defined thousands of years in advance.
It is a very complex calendar because every fourth year is a leap year, every seventh year a Shmita (Sabbatical year), every 49th or 50th year a Yovel (Jubilee), and so on. Its calculations are tied both to the sun and to the moon.
The Christian calendar is based solely on the rotation of the sun, the Islamic on the rotation of the moon, so their dates are different. The Jewish calendar, however, is based on the middle line,between the moon and the sun, and therefore is unchanged.
There is a highly precise calendar compiled as far back as the 4th century BC for the next 2,000 years of exile. It indicates the angular degrees, minutes, and seconds. It can currently be found on the Internet.
The need for such a calendar was based on the fact that Jews needed to know when to bless a month, a Sabbath, and so on. Therefore, they unerringly determined which day of the week would come, suppose, in 273 years, four months, and a certain number of days, the duration of day and night, the hours of sunrise and sunset, and so on.
They had a precise knowledge of the mechanics of the entire firmament. It is very interesting. When I first saw the book describing this calendar, I was amazed. It presents a variety of astronomical charts compiled 24 centuries ago.
From KabTV’s “Secrets of the Eternal Book” 10/12/16