1. What is the Nicaean Rule?

The Nicaean Rule (established at the First Council of Nicaea in 325 AD) determines the date of Easter as the first Sunday after the first full moon occurring on or after the vernal equinox (fixed as March 21).

2. How Does the Calculator Work?

The calculator uses the Nicaean rule algorithm:

Where:

• \( moon \) — First full moon after March 21
• \( equinox \) — Fixed as March 21

Explanation: The calculation involves a complex series of arithmetic operations based on the Metonic cycle, solar correction, and other factors to determine the exact date.

3. Importance of Easter Calculation

Details: Accurate Easter date calculation is crucial for the liturgical calendar, determining movable feasts, and coordinating church celebrations worldwide.

4. Using the Calculator

Tips: Enter any year between 1583 (Gregorian calendar adoption) and 9999. The calculator will determine the Catholic Easter date for that year.

5. Frequently Asked Questions (FAQ)

Q1: Why does Easter's date change every year?
A: Easter is based on a lunisolar calendar, combining both solar (equinox) and lunar (full moon) cycles.

Q2: Do all Christians celebrate Easter on the same date?
A: No, most Orthodox churches use the Julian calendar for calculation, resulting in different dates.

Q3: What's the earliest possible Easter date?
A: March 22 (last occurred in 1818, next in 2285).

Q4: What's the latest possible Easter date?
A: April 25 (last occurred in 1943, next in 2038).

Q5: Why does the algorithm start with year 1583?
A: This is when the Gregorian calendar was introduced; earlier dates would require Julian calendar calculations.