What is an equinox and what does it have to do with Easter?
Unlike other famous holidays, Easter doesn’t fall on the same date each year. It’s date is calculated. It falls on the first Sunday after the full moon after about March 21, the vernal equinox. Confused? Don’t be. The vernal equinox, is the day that day and night are about the same length of time. The equinox happens twice a year, the vernal and the autumnal . Usually around March 23 and September 23. The sun is directly overhead in both the Northern and Southern hemispheres. Wow, who knew? Therefore, the solar terminator, or edge between day and night is perpendicular to the equator. This is what makes the day and night roughly equal, hence, the dates are called equinoxes.
Ok, what else?
Not everyone uses the same calendar to calculate such things. We here follow the Gregorian calendar. Typically, the people who use the Julian calendar celebrate Easter a week or two after people in the West. Dizzying isn’t it? On we go! the Julian calendar assumes that a year is equal to 365.25 days. The Gregorian calendar assumes it is actually eleven minutes less. Got all that? Good!
Most of the world uses the Gregorian calendar. However, the most notable hold-out countries are: Afghanistan, Iran, Saudi Arabia, and Ethiopia. There are about forty calendars in use in the world. Most of them are used to determine religious holidays.
There are basically three types of calendars, solar, lunisolar, and seasonal. In addition some include the ever popular calendars with “years” of a fixed length. Many of the non-Gregorian calendars actually are exactly the same but substitute local names for months. And they use different eras to calculate the date. Other countries, such as Saudi Arabia, use the Islamic calendar for all of their noteworthy dates.
In conclusion, depending on what calendar you use, you could celebrate a holiday every day of whatever year it is on your calendar!