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 These are the kind of things that stir about in your brain when you are completely withdrawn from the kind of social life most normal teenagers enjoy…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!

ody N biskit….bak when de wheel waz bout ta bee inn vented, de food servizz gurl had a child hood friend, her was borned three yeers later then her older brother; both jan ewe wary 19, de food servizz gurlz gram paw waz born on feb ewe wary 29th, sister of food servizz gurl waz born on fatherz day N knot veree often does it fall on that act shoo ul day again & FSG, her mom N her momz mom waz all borned ona diffrunt day but has had ther birthday fall on de same day { like monday} for like yeerz now ?? ~~~ N happee bee lated two dad N his sisturr ! 🙂 ♥♥

February 29th birthdays are cool! A long time ago at Mecca, we had two leap day babies working for us at the same time, which was very long odds for a group of only 150-some people. Sister’s birthday will fall on Fathers Day four times every 28 years, and in the exact pattern I mentioned in the post, with six, five, six and eleven year intervals. As for the birthdays of mom and grandma… any two dates from March-December that fall on the same day of the week that year will fall on the same day of the week EVERY year, The Fourth of July and Halloween will always be on the same day of the week….. every single year! It’s the same principle that keeps Xmas Eve and NYE on the same day each year, it’s just not as noticeable since those holidays aren’t in consecutive weeks…

I have a headache!! Geez, you and your damn math!!

You’re seriously smart, though.

I don’t know about that. There’s plenty of ways I’m a dumbass. I have always been pretty perceptive of patterns other people don’t notice, though…

Just take the compliment, you tool.

That would go against my modest nature and self depreciatory attitude…

I give up! You’re as dumb as a box of cornholes.

Wow!

The useless knowledge that’s out there…..

I just wanna say my birthday was on Sunday. Which is also the day of the week I was actually born on. Take your crazy flow charts or whatever that was and see if you can guess how old I am. (I think that’s impossible, but since I didn’t actually understand all that number stuff above, maybe you’ll prove me wrong.)

Well, working backwards with the formula, you could have been born in 2006, 2000, 1995, 1989, 1978, 1972, 1967, 1961, 1950, 1944….. probably going back way too far now! The trick with the formula works when you supply the date and year and I tell you the day of the week.I was always sharpest at figuring out the answers for July dates since I could use my birthday as a reference…

Makes sense. My year’s one of the two in the middle. 😊

Wow! My eyes glazed over at the first mention of numbers/math! But, it is so cool/interesting you and your sister were born on the same date! I’ve kept lots of wall calendars because of the cute pictures, and I have noticed they repeat every so often, so I use them again when it happens. Also, I was born on a Thursday…a Thanksgiving day, and every so often it falls on the holiday again! 🙂

And now you will know it falls on Thursday (and Thanksgiving, so long as it’s kept the fourth Thu of November) four times every 28 years, and will pop up in the 6-5-6-11 pattern. If you bought the right 14 calendars, you’d never need to buy a new one ever again since one of them would always match up with that year!

I gladly skipped through this, slightly nodding off – gave me a huge rush of nostalgia – back to my math school days …

This is the kind of math I always found fun….. long before algebra and calculus and graphing stupid curves made me hate it. And it’s practical, unlike a hyperbola…

Uh huh. So you and your sister have the same birthday and that’s cool. And on that note, I’m going to exit stage left before there’s some sort of test on the above information.

I’m sure there are apps for figuring out stuff like this now that compute much faster than the human brain, so that I know the actual math behind it is likely a waste now anyway… other than giving me a rare non-feature blog post.

LMAO!!!

I think you lost me on the second round of calculating. For this stuff, I have book with data, hour by hour for several centuries, probably one of the few pluses of astrological work. You can look up any time, any date, any minute covered by the book. I own the book because those calculations make me dizzy … but to be fair, I’m the worst person with math EVER. Anywhere.

I always have an issue crossing those century years that aren’t leap years, and would probably find that book to be fascinating. And of course, if you go back far enough, you have to account for the British adoption of the Gregorian calendar in 1752… which changed George Washington’s birthdate from February 11, 1731 to the February 22, 1732 we all learned in school!

Happy Belated Birthday. I knew it, yet I blew it. Boo.

Thanks. No problem, there’s always next year!

Ok, that made me tired so I’m going to bed now. LOL

Even my bad posts have the practical use of curing insomnia!

Hey, I like nerdy shit! One of my favourite things I’ve learned from your blog is the anaconda ribbon on the globe thing.

I cannot stand Marilu Henner and her constant crowing about her highly superior autobiographical memory. She brags about being able to remember every day of her life, but the only thing she ever offers up is what day of the week a certain is. Every time she spouts that bullshit on some show, I scream to whoever has the unfortunate luck of watching with me that I know some cat on the internet that can do the same damned thing and it’s nothing but a math thang. An very impressive parlour trick that I have not the first clue about how to do myself, but a parlour trick nontheless…..

Only a rain man is gonna remember every day of their life. Hell, on this four day vacay I can’t even tell you what I did Monday. My high school geography teacher would be proud to know that his analemma lesson he spent a whole hour long class on 25 years ago is still enlightening people all this time later!

ouch… math…. but it’s cool to have a birthday with your sis ;o) I often celebrated with my cousins who have their birthday the next and the after next day… we had one party and it was always like war, they were older than me and their bully-friends ruined everything… sigh…

My family has so many birthdays bunched up in the summer (and especially July) that it’s unreal. You can go broke on all the parties and gifts even before Christmas comes around…

You have way too much time on your hands 🙂

I can’t wait to try this out at my next social gathering, though (I challenge you to calculate which decade that might be in). I think I have this right, let’s see, multiply by 7, carry the one, divide by a banana, take away the number you first thought of… and the answer is… aardvark!

You forgot to factor in the leap possum….

He leapt straight off a cliff so we don’t have to worry about him.

……zzzzzzzzzzzzzzzzzzzzzz……Math………zzzzzzzzzzzzzzzzzz……….

Pam

This is why everyone flocks to Professor Sam and Teddy’s class rather than mine! I can’t keep the subject interesting….

I HATED math…..I did great in “non-important” things like art class but math simply did not interest me. Good thing I’m not in banking huh?

Pam

Whoa. Who’d have thunk it? All this math whiz is way beyond my simple brain…so I’ll just take your word for it. 🙃

It would be a whole lot easier if we all had 28 fingers and toes…

I’ll take your word for it also! Ya lost me after the Birthday thing…. Bummer! sharing a birthday with your sibling would suck!! It’s your day, not theirs!! Very interesting SUBJECT…! 🙂

Eh, she can have it! I’ll pick a different birthday…. like the 12th of Never!

Happy very belated birthday! I love this stuff. Thanks for the explanation. My brain’s been a little off lately so I’m going to write that down. I forget the year (I will have to use the formula!) but one year starting in March I used a 1992 Beatles calendar because all the days matched up perfectly. Now I know why! Awesome. I love these posts.

Happy birthday, ES!

You’ve got to set your Tivo, VCR or whatever for this show coming in 2018:

http://screenrant.com/marvel-new-warriors-squirrel-girl-explained/