Why Do Books Publish on Tuesdays?

Why do books get published on Tuesdays? I have a book coming out in June, The Boy Who Loved Math, and yes, it's June 25th, a Tuesday. I looked back to when my novel Intentions pubbed--August 14th, a Tuesday. I didn't always know this; in fact I just found it out this past year.  I wish I could remember who told me. But the other day I was talking to Ziki, the man who sticks needles in me to make my back and leg pain go away. We made an appointment for the next week (tomorrow) and I told him that afterwards I would be going to a book party for my friend Marguerite's new book:











"But it's not a Tuesday," he said. I told him a book party doesn't have to be on the release date--but wait, how did he know that?  He wasn't sure, he just did. He said that albums always had a day to release (he thought Fridays, and maybe it used to be so, but now it seems CDs and DVDs of movies release on Tuesdays, too).



I asked a few people, and no one seemed to know. I posted my question on twitter and got these answers:



Tradition based on coverage in Sunday papers and getting books on shelves is my understanding.



I asked: 

Are they reviewed the Sunday before or after. 



The answer: 



Before. So that booksellers get to spend Monday explaining why people can't buy the books they just heard about.



Hah. 





Other people chimed in with links: 



http://www.verlakay.com/boards/index.php?topic=64015.msg754277#msg754277



http://www.themillions.com/2009/06/ask-book-question-73-tuesday-new_09.html



http://www.fourhourworkweek.com/blog/2012/08/17/amazon-monthly-100/



And other answers: 



I've heard shipment was a factor--UPS boxes come Monday, scan & put out CDs, etc., Tue.



Probably a less busy day for most stores too. But no one seems to know for sure.





I'm 99.9% sure books are Tues b/c of Music release on Tues. So ? would be why music on Tues.



This might answer that question: 



http://rulefortytwo.com/secret-rock-knowledge/chapter-4/why-are-cds-released-on-tuesdays/ 





I read all of those (you don't have to) and it still seems to me that no one knows for sure... I asked some friends who are publishers and editors: nope. They didn't know.



And so I started thinking two things:



1. In the old days, I would have called a reference librarian. My old friend from the Doylestown library (where I used to live) would have found out for me, I know that for sure. So I decided to call the New York Public Library. Oops. I waited too long. It's Presidents' Day. Library closed. But it took me almost a week to remember that I used to talk to reference librarians for this sort of thing. Yes, kids, before the Internet. I used to go to the library, go up to the desk and say, "Jan, how do I find out the answer to this question?" And sometimes Jan would just find out for me, and sometimes she would teach me how to fish. I did this for a long time, even after there was The Internet, until it became more or less part of my right hand.



2.Will this change? Whatever is the cause, will Tuesdays as pub dates change if there are more ebooks and fewer bricks and mortar bookstores? Then will people release books willy nilly? Do people who self-publish books follow the Tuesday rule?



I'm really hoping that someone will post here and tell me... Why do books publish on Tuesday? I've just spent so much time on this... as so often happens when one (me) gets stuck on a research treadmill. I just want to know the answer!



Uh oh. Wait a minute. I just looked up Marguerite's book and it officially published YESTERDAY. Which was Monday. According to Amazon. And B & N. Her publisher just says February. Okay, now I'm really confused.