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"the basic rule for Easter is that it falls on the first Sunday after the first full moon of Spring (that is, the first full moon after the Spring Equinox)" Gi

"the basic rule for Easter is that it falls on the first Sunday after the first full moon of Spring (that is, the first full moon after the Spring Equinox)" Given that the watch knows all these parameters (i.e. day of the week, moon phase and date (Mar 21 = Spring equinox), would it be possible to construct a mechanical complication that calculates the Easter date?

scblock 9y ago
The article goes into that as it discusses the mechancial computus in the clock at the cathedral at Strasbourg, in Alsace, France.
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stephen_g 9y ago
Wouldn't that only mean you'd be able to work out if it is Easter Sunday? So you could show an indicator on the day but it's a much harder problem to have it work out the right date for the next occurance from the start of the year (or from the last Easter Sunday).
- f_allwein 9y ago
  No - there's a finite amount of possible dates (between March 22 and April 25), so every year could have a numeric value for the Easter date that the pointer could point to.
CamperBob2 9y ago
I don't understand this, myself. Why isn't this calculation implemented as a mechanical state machine? It's impossible to implement a 5,700,000-year cycle with an individual program wheel, but three or four smaller, simpler ones should be able to do the job. Hard to see why this is considered a difficult problem at this point, 2000+ years after the Antikythera Mechanism.
- ZoeZoeBee 9y ago
  They mentioned it in the article. It is impossiblly difficult to know all of the variables which cause a time shift over a period of time as long as 5 million years. You could build it but you'd most likely be wrong eventually, failing to compensate for the unknowns >The date of Easter encodes a strange kind of orderly disorder, and yet, even that is an expression of an abstraction that only approximates reality. Over a period of 5,700,000 years, as Bryan Hayes points out in his 1999 article on Y2k compliance and the Strasbourg clock, things like tidal drift will cause enough variation in the orbital and rotational periods of the Earth that any algorithm will require ad hoc correction anyway
  - CamperBob2 9y ago
    But that's not the issue at hand. The watch needs to last a few hundred years or a couple thousand at most, not 5 million. At those timescales the problem is quite deterministic and perfectly solvable, especially when the mechanism is already keeping track of the date and lunar phase. A mechanism that only works for 28 years shouldn't have been contemplated by a company that literally advertises their products as heirlooms.

scblock 9y ago

The article goes into that as it discusses the mechancial computus in the clock at the cathedral at Strasbourg, in Alsace, France.

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stephen_g 9y ago

Wouldn't that only mean you'd be able to work out if it is Easter Sunday? So you could show an indicator on the day but it's a much harder problem to have it work out the right date for the next occurance from the start of the year (or from the last Easter Sunday).

f_allwein 9y ago
No - there's a finite amount of possible dates (between March 22 and April 25), so every year could have a numeric value for the Easter date that the pointer could point to.

CamperBob2 9y ago

I don't understand this, myself. Why isn't this calculation implemented as a mechanical state machine? It's impossible to implement a 5,700,000-year cycle with an individual program wheel, but three or four smaller, simpler ones should be able to do the job. Hard to see why this is considered a difficult problem at this point, 2000+ years after the Antikythera Mechanism.

ZoeZoeBee 9y ago
They mentioned it in the article. It is impossiblly difficult to know all of the variables which cause a time shift over a period of time as long as 5 million years. You could build it but you'd most likely be wrong eventually, failing to compensate for the unknowns >The date of Easter encodes a strange kind of orderly disorder, and yet, even that is an expression of an abstraction that only approximates reality. Over a period of 5,700,000 years, as Bryan Hayes points out in his 1999 article on Y2k compliance and the Strasbourg clock, things like tidal drift will cause enough variation in the orbital and rotational periods of the Earth that any algorithm will require ad hoc correction anyway
- CamperBob2 9y ago
  But that's not the issue at hand. The watch needs to last a few hundred years or a couple thousand at most, not 5 million. At those timescales the problem is quite deterministic and perfectly solvable, especially when the mechanism is already keeping track of the date and lunar phase. A mechanism that only works for 28 years shouldn't have been contemplated by a company that literally advertises their products as heirlooms.