Why do Jewish holidays change their date

Question

Let’s say rosh Hashanah. It varies it’s date every year, but if the Jewish calendar is a fixed amount of days, wouldn’t it be earlier and earlier or later and later every year?

In: 4

Answer 1

Jewish calendar uses lunar cycles to define months—12 of them that are 29-30 days long. It then adds in a leap month in certain years to re-center the calendar to the solar cycle.