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This is a really silly application. It tells you the date of Easter Sunday in any year in the range 1583 to 4099. And that's it!
The mathematical method of calculating an Easter Date (Latin: Computus) for any year in the range 1583 to 4099 is rather complicated. I reccommend a search on the internet which would explain it all better than could I.
Generally, the first Sunday after the full moon that falls on or just after the Spring Equinox (March 21) is fixed as Easter. Easter, thus, is also known as a moveable feast, since it can, according to those rules, occur on any date between March 22nd and April 25th. It can never occur earlier than March 22nd due to the rule, nor later than 25th April due to the Moon's orbital period. The earliest is if the full moon occurs on Saturday 21st March, so Easter Sunday is the following day. The latest is if the full moon is one day earlier, 20th March which has to be a Saturday. The next full moon would then be (plus 29 or 30 days) Sunday 18th April, and so Easter Sunday is the next Sunday after that, i.e. 25th April. Since the Moon's orbital period varies, even this is a bit of a simplification.
To date (2008), there exists a difference of opinion between the churches of the West and the more orthodox churches of the East, which are deeply influenced by the old traditions. At a summit in Aleppo, Syria, in 1997, the World Council of Churches put forward the latest of many suggestions to restructure the methods of determining the date of Easter to remove this difference of dates between the Western and the Eastern Churches. Easter would be defined as the first Sunday following the first astronomical full moon following the astronomical vernal equinox, as determined from the meridian of Jerusalem. The reform would have been implemented starting in 2001, since in that year the Eastern and Western dates of Easter would coincide. Unfortunately or not, depending on your viewpoint, it failed due to a lack of support from the Eastern churches who were suspicious of the motives of the Western. Should reform be implemented, this calculator may no longer hold true.
At the time of compiling this software (2008) another initiative is being proposed, but any introduction would be years away.
This calculator uses the traditional Western methods, as described by the user clicking the button marked "Algorithm", but due to limitations in the mathematics, the Moon's orbital position becomes slightly in error over the years, until in 4099, the algorithm would need to be amended. If you need to know the date for post year 4099, then I'm afraid I have failed you with my software.In the latest version (1.03) the Algorithm button no longer displays the algorithm, so I have reproduced it below.
Anonymous Gregorian algorithm
"A New York correspondent" submitted this algorithm for determining the Gregorian Easter to the journal Nature in April 1876. It has been reprinted many times, in 1877 by Samuel Butcher in The Ecclesiastical Calendar, in 1922 by H. Spencer Jones in General Astronomy, in 1977 by the Journal of the British Astronomical Association, in 1977 by The Old Farmer's Almanac, in 1988 by Peter Duffett-Smith in Practical Astronomy With Your Calculator, and in 1991 by Jean Meeus in Astronomical Algorithms. There does not appear to be a range limitation with this method, but since it gives precisely the same dates as another algorithm I have that does specify a range, I have retained the 1583 to 4099 validity range in my program.
| Expression | Y = 1961 | Y = 2009 |
| a = Y mod 19 | a = 4 | a = 14 |
| b = floor (Y / 100) | b = 19 | b = 20 |
| c = Y mod 100 | c = 61 | c = 9 |
| d = floor (b / 4) | d = 4 | d = 5 |
| e = b mod 4 | e = 3 | e = 0 |
| f = floor ((b + 8) / 25) | f = 1 | f = 1 |
| g = floor ((b - f + 1) / 3) | g = 6 | g = 6 |
| h = (19a + b - d - g + 15) mod 30 | h = 10 | h = 20 |
| i = floor (c / 4) | i = 15 | i = 2 |
| k = c mod 4 | k = 1 | k = 1 |
| L = (32 + 2e + 2i - h - k) mod 7 | L = 1 | L = 1 |
| m = floor ((a + 11h + 22L) / 451) | m = 0 | m = 0 |
| month = floor ((h + L - 7m + 114) / 31) | month = 4 (April) | month = 4 (April) |
| day = ((h + L - 7m + 114) mod 31) + 1 | day = 2 | day = 12 |
| Gregorian Easter | 2 April 1961 | 12 April 2009 |
The application does quote an Excel formula which does the same thing, though I am not sure of the validity range. All you have to do is open a new Excel spreadsheet, type a year in cell A1, format cell A2 as "Date" and paste into cell A2 the following formula:
=DOLLAR(("4/"&A1)/7+MOD(19*MOD(A1,19)-7,30)*14%,)*7-6Too simple? It does work, but I don't know how! If you are too lazy to do this yourself, there is a link below to a spreadsheet for you.
| WARNING : DOWNLOADING ANY FILE SIGNIFIES ACCEPTANCE OF THESE TERMS AND CONDITIONS! | ||||||
|---|---|---|---|---|---|---|
| File Download Link | Version | Filename | Filesize | Download Time* | Screen Size | Comment |
| Easter Calculator Executable | 1.04 | "Easter.exe" | 2.8MB | 20 secs | 810W 547H | Made a few simple changes. |
| Easter Calculator Spreadsheet | 1 | "Easter.xlsx" | 8KB | 2 secs | 382W 308H | None really! |
* The download time shown is approximate for connections with two speeds. The fastest would be fibre broadband, and corresponds to my current speeds with BT Infinity. The slower value was a non-fibre broadband connection I previously had with Talk-Talk. Both are based on the "upload" time for me to load the file onto my web-site using Filezilla [version 3.33.0]. You can easily test your own broadband speed by downloading the free application "Network Speed" from the Windows App Store.
The image below is a grab from the application.
Unfortunately, I do not have any means of establishing the minimum hardware specification required to run my software. All I do know is the specification of my computer, on which the software was developed, tested and which runs satisfactorily.
Original Computer specification:
In May, 2018, I purchased a new PC with a significantly upgraded specification:
* I have tried to design my software to present a smaller window size than my monitor permits, as I am concious that many people will have a smaller monitor than listed above. I will provide the maximum window size I use with each application's details.
If you use the software on a PC with a different set up, let me know if you have any issues with running the application, and if it works and you have the time, please let me know what your specification is. It should work on all flavours of Windows from SP, Win7 to Win10. I did have a lot of memory in my original set up - well, 4 GB was a lot in 2010!
I need to include something for this, but it won't be a miles long "Agreement" that you see with most software these days. "File(s)", "Software" and "Application" have the same meaning herein. "You" are the person who downloaded the file(s) from this web-page, and these conditions also apply to anyone to whom you pass on the file(s).
Terms compiled and added to web-page 19th October, 2016.