As you may remember, I
celebrated had a birthday on the 13th last week. I have a sister whose birthday is also on July 13th. She was born on my fifth birthday. It is not common at all for non-twin siblings to share a birthday…. think about it. The average American family has something like 2.1 children, and there are 365.25 possible birthdays out there. I’m too stupid to try and figure out that kind of probability math, but shared sibling birthdays are obviously a rare occurrence for those who didn’t also share a womb…
Making the birthday match between me and Sis #2 even freakier is the fact that we were both born on a Sunday. That’s a crazy kind of coincidence there. So crazy, in fact, that it piqued my interest in how our Gregorian calendar cycles around and around through the years. How often do certain dates reoccur on the same days of the week, and is there a pattern that guides them as they gradually shift to the right on our calendars each ensuing year? These are the kind of things that stir about in your brain when you are completely withdrawn from the kind of social life most normal teenagers enjoy…
I got to thinking about this again this morning because today is Wednesday July 19th… a day/date combination that likely means less than zero to you, but that is indelibly burned into the captain’s log of my mind thanks to the freak storm from hell I had a front row seat to… one of those significant events that locals will still be telling their great grandkids about 80 years from now when you’ll be able to control the weather with an app. This is the first time July 19 has fallen on hump day since 2006…. 11 years ago.
So wait… me and my birthday sharing sister can be born on the same day five years apart, and yet we have this instance where it takes 11 years to get that same kind of synergy between day and date? What the fuck is up with that?
I love it when I can reuse an image without having to change the caption…
It’s hard to believe that in over five years of blogging that I have yet to share my knowledge of the beautifully symmetrical 28 year cycle our calendar incessantly fails to repeat (at least in our lifetimes) time and time again. Maybe that’s because I know that drawings of possums getting disemboweled and playing obscurely shitty earworms are the kinds of things that the average person will at least take the time to check out before they carefully scan for the floating unfollow button. Nobody wants to listen to someone who is extremely geeked up about some subject the rest of the world gives absolutely no fucks about ramble on and on about things like symmetrical beauty and day/date cycles, after all….
Well, that’s just too damn bad then….. because you’re going to listen to my nerdy ejaculations about the calendar cycle today, and you’re damn well going to like it!!!!
There are 365 days in a normal year, which divides into seven with a remainder of one. This is why, in most years, the dates will universally creep forward one day later. My birthday was on a Thursday this year… next year it will be on Friday the 13th. Woohoo! And, for the purposes of pretty much every adult alive today, every fourth year will have that extra added bonus we like to call leap day. After each occurrence of February 29th, the next 365 days will all bump forward TWO days of the week due to the additional day. Are we clear so far?
Now, let’s take the year 2017 since it just conveniently happens to be that year right now. For the sake of this post, let’s pretend you wanted to know what the next year will be when July 19 returns to falling on Wednesday. Using the information we learned above….
2017 – Wed
2018 – Thu
2019 – Fri
2020 (Leap year) – Sun
2021 – Mon
2022 – Tue
2023 – Wed!
So, in six years we will see the year 2017 repeat all over again. Well, maybe not the events of this year…. but at least the days will line up all nice and perty again.
OK, that’s a six year jump. What about the next time after that when we get a Wed. July 19?
2024 (Leap year) – Fri
2025 – Sat
2026 – Sun
2027 – Mon
2028 (Leap year) – Wed!
Hey, only five years this time! And this exactly how me and my sister wound up both being born on a Sunday… as I was born in 1975 (a year before a leap year, just like 2023) and she was born in 1980 (A leap year, just like 2028).
Shall we continue?
2029 – Thu
2030 – Fri
2031 – Sat
2032 (Leap year) – Mon
2033 – Tue
2034 – Wed!
And we get another six year jump! I’ll bet you know what’s coming next…
2035 – Thu
2036 (Leap year) – Sat
2037 – Sun
2038 – Mon
2039 – Tue
2040 (Leap year) – Thu
2041 – Fri
2042 – Sat
2043 – Sun
2044 (Leap year) – Tue
2045 – WED!!!!
Yep, there’s the 11 year jump that was also present between 2006 and 2017. Once again, it isn’t just dumb luck that both starting years (2006, 2034) were even non-leap years and both closing years (2017, 2045) are years after a leap year. There’s a definite pattern here…
SIX – FIVE – SIX – ELEVEN! Which number you use to go forward or backward to find the next year with that same pattern of days depends on which type of year you are starting with….
- Year AFTER a leap year (Y1)- go forward six years (Y3) or backward eleven (Y2)
- Even NON-leap year (Y2) – go forward eleven years (Y1) or backward six (Y4)
- Year BEFORE a leap year (Y3) – go forward five years (Y4) or backward six (Y1)
- Leap Year (Y4) – go forward six years (Y2) or backward five (Y3)
You need to think of “years” as running from March – February for any calculation involving a leap year to “make sense”…
By the way… 6 + 5 + 6 + 11 = 28… which not too coincidentally is also the result of seven (Number of days in a week) times four (The leap year period). Yes, the calendar repeats every 28 years between 1901 and 2099! If you aren’t sure what day of the week you were born on, wait until your 28th birthday! Or, for us mature types, your 56th will do. And yes, even your 84th birthday is guaranteed to fall on the day of the week you were born!
And here’s where that beautiful symmetry jazz I was foaming about comes in…. in ANY span of 28 years during the 20th and 21st centuries, every date in the calendar will fall on each day of the week EXACTLY four times (One time for February 29th, which recedes “backwards” two days with each occurrence). How cool is that?
And now that you know the 6-5-6-11 pattern, you can amaze your friends by letting them know exactly which four years this very day and date will meet up in again! Or the past years it had previously paired up in! If you’re one of those people whose grey matter is a vast wasteland of day/date combos from the past, it’s even possible to easily calculate the day of the week any day between 1901 and 2099 happened in your head simply using multiples of 28 and 6-5-6-11ing your way through the years! With this nifty trick you learned today, it’s a cinch you’ll be the life of the party!