Easter Date
This applet will work out the date of Easter Sunday for any year, using an algorithm devised by T O'Beirne in 1961, which he called "Ten Divisions to Easter". Below that is a spreadsheet version of the algorithm being implemented.
Choose for which year you are interested in finding the date of Easter Sunday.
Year 
Ideas for Teachers
Introduce the lesson with trying to find the date of the next Easter, and a discussion of why it is hard to do. Then bring up the activity, and type in the year to find the date. How does the program work? A discussion of algorithms, and their applications to computers is a natural follow on, before introducing the actual algorithm in the worksheet. Getting your students to go through the algorithm once manually is definitely worth while for two reasons: they will have to use some good mathematical skills; they will appreciate computers and how they work a lot more. Finally, let them loose on Excel to create a program that will generate the same results.
Introduce the lesson with trying to find the date of the next Easter, and a discussion of why it is hard to do. Then bring up the activity, and type in the year to find the date. How does the program work? A discussion of algorithms, and their applications to computers is a natural follow on, before introducing the actual algorithm in the worksheet. Getting your students to go through the algorithm once manually is definitely worth while for two reasons: they will have to use some good mathematical skills; they will appreciate computers and how they work a lot more. Finally, let them loose on Excel to create a program that will generate the same results.
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This is a great resource from the MEP Project run by CIMT a few years ago. All their resources are available online. It provides an algorithm to calculate the date of Easter for any year.
This is an Excel Spreadsheet that will calculate all the terms of in the above activity. It is fairly easy to create from scratch, and is a good activity for pupils to engage in after working through the activity.
