What constitutes a classic novel?

I've taken many English courses in my life, and I have had to read some of the most classic pieces of literature known in society. This question crossed my mind today as I was sitting in the bookstore and just happened to glance at the section entitled "Literary Classics." What exactly constitutes a work of literature as a classic? Stories like To Kill A Mockingbird, The Scarlett Letter, Walden, The Adventures of Huckleberry Finn and Tom Sawyer, The Great Gatsby, and the list could go on and on. What makes these novels so beloved by so many people and places them in the category of literary classics. Is it because they're so well-known. I did some digging because I was looking for these very answers and I came across this website:http://www.articlesfactory.com/articles/education/qualities-of-classic-literature.html(This website goes into depth about what constitutes a classic. First, a classic has to be timely but it also has to be timeless. A classic novel has to reflect the times that it was written in. There's more characteristic gems like this in the article.)  I love classic literature. Some people may read classics to make themselves seem smarter or well-rounded. I don't know. I just think classics give a sense of prestige and makes one feel well-educated and knowledgeable. Below I have posted a link of over 100 classic works of literature. It would be a fun challenge to see how many of these you can read! I might even challenge myself.http://eagleforum.org/educate/1997/june97/list.html