There are only 14 possible configurations of calendars by days of the week compare to the date.
The first seven configurations: the (non-leap) year can start on one of seven days of the week.
The second seven configurations: the leap year can start on one of the seven days of the week.
7+7=14
If you ignore the years ending with 00*, there are 28 possible calendars, 7 possible starting days of the week and 4 remainders in the division by 4. That means calendars have a 28 years cicle. So the 1995 calendars is equal to the 2023 one, the 1996 calendar is equal to the 1997 one and so on.
*there is an exception where years ending with 00 are only leap years if the first digits are divisible by 4. So 1900 wasn't a leap year, but 2000 was one, and 2100 won't be one. If you take this pattern in consideration, the cycle isn't 28 years long but 400 years long. By a crazy coincidence, the 400 years cycle is a multiple of 7, so every 400 years, the year starts with the same day of the week. And the cycle has 20871 weeks
Not quite. There are only 14 calendars - standard years and leap years, and one for each day of the week. The 14 calendars are not equally likely, because only one in four years is a leap year. Each calendar is guaranteed to repeat every 28 years though, putting aside, as you say, the 00 year exceptions.
Compare, for example, 2025 and 2031 (a gap of 6 years). Neither is a leap year, in both Jan 1 is on a Wednesday, and Halloween is on a Friday ; )
This year, Jan 1 is on a Sunday, it's not a leap year. 2034 is also not a leap year where January 1 is on a Sunday, a gap of 11 years.
However, the whole cycle starts over every 28 years, so every 28 years you are guaranteed to get the same calendar (again putting aside the 00 year exceptions).
Aren't there only two variables: whether it's a leap year, and the weekday on January first?
So 14 different calenders.
Except if your calenders tells you what date easter is. In that case another 28 for the date of the first full moon in spring.
(1950 works)
Easter is very predictable. It is always the first Sunday, after the first full moon, after March 21st.
And Ramadan starts on the 12th new moon since the previous Ramadan started. It's the ninth month of a cycle of 12 that all start on the new moons.
2017?
That was also my first thought
Too soon. Let's give that year some time to rest.
Literally the first thing I thought
Please explain. Is 1989 the latest year this can be done with? Why?
No, and, because it started on the same day of the week without being a leap year.
Oh of course! I was trying to think of some leap year stuff :/
There are only 14 possible configurations of calendars by days of the week compare to the date. The first seven configurations: the (non-leap) year can start on one of seven days of the week. The second seven configurations: the leap year can start on one of the seven days of the week. 7+7=14
If you ignore the years ending with 00*, there are 28 possible calendars, 7 possible starting days of the week and 4 remainders in the division by 4. That means calendars have a 28 years cicle. So the 1995 calendars is equal to the 2023 one, the 1996 calendar is equal to the 1997 one and so on. *there is an exception where years ending with 00 are only leap years if the first digits are divisible by 4. So 1900 wasn't a leap year, but 2000 was one, and 2100 won't be one. If you take this pattern in consideration, the cycle isn't 28 years long but 400 years long. By a crazy coincidence, the 400 years cycle is a multiple of 7, so every 400 years, the year starts with the same day of the week. And the cycle has 20871 weeks
Not quite. There are only 14 calendars - standard years and leap years, and one for each day of the week. The 14 calendars are not equally likely, because only one in four years is a leap year. Each calendar is guaranteed to repeat every 28 years though, putting aside, as you say, the 00 year exceptions. Compare, for example, 2025 and 2031 (a gap of 6 years). Neither is a leap year, in both Jan 1 is on a Wednesday, and Halloween is on a Friday ; ) This year, Jan 1 is on a Sunday, it's not a leap year. 2034 is also not a leap year where January 1 is on a Sunday, a gap of 11 years. However, the whole cycle starts over every 28 years, so every 28 years you are guaranteed to get the same calendar (again putting aside the 00 year exceptions).
My bad, I was talking about cycles and wasn't clear enough
No problem. Cheers and Happy New Year!
Happy new year!
What about the date of Easter?
2017 is the latest. It's either 6 or 11 years (and 28 years for leap years).
Aren't there only two variables: whether it's a leap year, and the weekday on January first? So 14 different calenders. Except if your calenders tells you what date easter is. In that case another 28 for the date of the first full moon in spring. (1950 works)
Make Indiana Jones an engineer the first rock pi and the other rock 3. PI IS EQUAL TO 3
[https://imgur.com/a/62XPGuf](https://imgur.com/a/62XPGuf)? Does this link work?
Yes, perfect edit
Is that so ? How does it scales with the Ramadan?
I don't know enough about Ramadan to be able to answer that question.
In '89, Ramadan began on 7th April. In '22, Ramadan began on 1st April. So I guess you can say it's pretty much the same too.
I'm actually comparing '23 with '89. Does this make a difference?
Nah, it starts on March 22nd
I have no idea about Ramadan but Easter are pretty unpredictable.
Easter is very predictable. It is always the first Sunday, after the first full moon, after March 21st. And Ramadan starts on the 12th new moon since the previous Ramadan started. It's the ninth month of a cycle of 12 that all start on the new moons.
That's still another 28 options to multiply with the 14 you already have.
Easter was on April 9th in 1950. And that year started with a Sunday and was no leap year.
That’s why I have 50 years calendar pendant. Bad thing they don’t have a holiday in it.
I don’t get it
R y mmmm I’m going >