It was 15 years ago that Twister changed America's summer blockbuster season. It didn't do it with cutting-edge special effects or immersive 3D technology or previously unknown storytelling devices. No, Twister altered something more fundamental about summer: its start date.
Before 1996, the summer movie season began with Memorial Day Weekend, at the end of May. There was no official decree, nothing in the Hollywood city ordinances, but that's how it worked. The trend began with Star Wars in 1977, and subsequent Memorial Day releases included Alien, The Empire Strikes Back, Rocky III, Return of the Jedi, Indiana Jones and the Temple of Doom, Rambo II, Beverly Hills Cop II, Crocodile Dundee II, Indiana Jones and the Last Crusade, Back to the Future Part III, Backdraft, Alien 3, Cliffhanger, and The Flintstones.
In the 1990s, with the Memorial Day kickoff firmly established, some studios started opening tent-pole films a week early, to beat the rush. Lethal Weapon 3 (1992), Maverick (1994), and Die Hard: With a Vengeance (1995) all opened the third weekend in May and earned fourth-weekend-in-May-style grosses.
Then, in 1996, Warner Bros. had a crazy idea. Memorial Day was going to be owned by Paramount's Mission: Impossible. What if WB opened Twister not one week early but -- and stay with me here -- TWO weeks early? Twister had Spielberg as an executive producer, it was about natural disasters, and it was fun but kind of stupid: It was clearly a "summer movie." To open it a fortnight ahead of the customary summer movie season would be a bold move. WB said, "Screw it, WE'RE DOING IT." Go big or go home, that's what they say at Warner Bros.
And it worked. Twister opened to $41.1 million, at that time the biggest debut ever for a non-summer release. It went on to be the second highest-grossing film of all of 1996, behind Independence Day. More importantly, it signaled a shift. With Twister having tested the waters, other movies followed suit and opened earlier in May, effectively changing the start of the summer blockbuster season. Fifth Element did it in 1997, followed by Deep Impact, The Mummy, Gladiator, and The Mummy Returns. In 2002, when Spider-Man debuted on May 3 and had the best opening weekend EVER, any question about summer's start date was erased. At the movies, summer starts the first weekend in May.

To commemorate the 15th anniversary of this seismic shift in cinematic calendaring, we took a look at the five top-grossing films of each summer since then, with "summer" now being defined as May-August. The five most popular movies from each summer, 1996-2010, gives us 75 movies total. We'll call them the Summer 75. What do these 75 warm-weather flicks tell us about our summertime tastes? Let's investigate.
The most obvious trend is in the ratings. Among the Summer 75, 49 movies are rated PG-13. Only 10 are rated R, and not one of those was the highest-grossing movie of its summer. (In fact, ranking the Summer 75 according to gross, you have to go all the way down to #27 before you hit an R rating: The Matrix Reloaded.) Five G-rated films are represented, four from Pixar and one from Disney (Tarzan). The remaining 11 PG's are mostly related to Shrek, Harry Potter, or Star Wars.
Sequels are big in the summertime. Everyone knows that. It's in the Bible. Indeed, 31 of the Summer 75 are sequels (or prequels), and another five are remakes (or reboots).
The vast majority of these 75 movies are based on pre-existing properties, including 13 from comic books, 13 from novels, three from TV shows, two from toys (Transformers), and three from an amusement park ride (Pirates of the Caribbean). (No stage plays, board games, or Bazooka Joe comics ... yet.) How many are wholly original -- not based on a book, not a sequel or remake, but written directly for the screen? Just 26, or about one-third.
Films aimed at women have been making great strides in the summertime, and while that's true, those strides have not been enough to make a dent on the list. The Summer 75 has exactly two (2) movies targeted at a female audience: My Best Friend's Wedding and The Twilight Saga: Eclipse. Movies like Sex and the City and The Devil Wears Prada were definitely hits, but neither was among the top five earners in its summer.
There are no horror films in the Summer 75. The closest would be a couple of chillers -- Signs and The Sixth Sense -- and a spoof, Scary Movie.
Not much reality, either, as you might expect. Only two members of the Summer 75, Saving Private Ryan and Pearl Harbor, are based on actual historical events. A third, Gladiator, while not a true story, is set in a more or less believable version of history.
Aliens, though. Aliens are big in the summertime. They attack Earth (Independence Day, War of the Worlds, Signs), they send orphans to help us (Superman Returns), and they have wars amongst themselves (the Star Wars prequels). All told, there are 14 movies in the Summer 75 that involve non-Earthlings.
Ten films on the list are animated, including five from Pixar, three from Dreamworks (all with the word "Shrek" in the title), one from non-Pixar Disney (Tarzan), and one from Universal (Despicable Me).
There are 13 movies on the list, representing six different franchises, that have further entries coming out this summer alone: Pirates of the Caribbean, Harry Potter, Transformers, X-Men, Cars, and The Hangover. The list also includes the franchises of Batman, Men in Black, Twilight, Star Trek, Spider-Man, Superman, Jason Bourne, and Mission: Impossible, all of which have sequels in production. In other words, take a good look at the Summer 75, because you're going to see about 40 percent of those titles on theater marquees within the next two years.
The highest-grossing movies of the summer tend to be among the highest-grossing movies of the entire year, but not always. There are usually strong showings from spring, fall, and winter releases too, like Avatar and Lord of the Rings. In fact, 2007 and 2008 are the only years in history where the top five movies of the year were all summer releases. And there's never been a year in which summer movies comprised the entire top 10. So don't get too full of yourself, summer! You don't rule the world yet.
Within the Summer 75...
Number of May releases: 29
Number of June releases: 20
Number of July releases: 23
Number of August releases: 3
Number of films supposedly set in the real world as we know it, with no supernatural, sci-fi, or fantasy elements: 17 (e.g., The Perfect Storm, Air Force One; several comedies like The Hangover and There's Something About Mary)
Number of films in which one of the credited speaking roles is the President of the United States: 9 (all fictional except FDR in Pearl Harbor)

Number of superhero-based films: 12 -- 3 DC, 7 Marvel, and one that's neither (Hancock).
Number of films centered on natural disasters: 5 (i.e., The Perfect Storm, Twister, Armageddon, The Day After Tomorrow, Deep Impact)
Number of films centered on animals or in which animals are a significant part of the story: 9 (e.g., The Lost World: Jurassic Park, the Shrek movies, Doctor Dolittle)
Number of films nominated for the Best Picture Academy Award: 6 Saving Private Ryan, The Sixth Sense, Gladiator, Up, Inception, Toy Story 3
Number that won it: 1 (Gladiator)
Appearances by Johnny Depp: 4 (playing Jack Sparrow three times and Willy Wonka once)
Harrison Ford: 2 (Indiana Jones and the Kingdom of the Crystal Skull, Air Force One)
Will Smith: 4 (Independence Day, Men in Black, Men in Black II, Hancock)
Nicolas Cage: 2 (The Rock, Face/Off)
Eddie Murphy: 6 (three Shreks, plus The Nutty Professor and Doctor Dolittle)
Bruce Willis: 2 (Armageddon, The Sixth Sense)
Mike Myers: 5 (three Shreks and two Austin Powerses)
Tom Cruise: 4 (Mission: Impossible, Mission: Impossible II, War of the Worlds, a cameo in Austin Powers in Goldmember)
Morgan Freeman: 5 (Deep Impact, Bruce Almighty, Batman Begins, The Dark Knight, and narrator in War of the Worlds)
Samuel L. Jackson: 5 (three Star Wars prequels and both Iron Man films)
Steven Spielberg (director): 4
Steven Spielberg (producer): 8
Jerry Bruckheimer (producer): 6
Michael Bay (director): 5

The Top 5 Movies of Each Summer, 1996-2010
(All totals are U.S. grosses and are courtesy of Box Office Mojo.)
1996:
Independence Day $306,169,268
Twister $241,721,524
Mission: Impossible $180,981,856
The Rock $134,069,511
The Nutty Professor $128,814,019
1997:
Men in Black $250,690,539
The Lost World: Jurassic Park $229,086,679
Air Force One $172,956,409
My Best Friend's Wedding $127,120,029
Face/Off $112,276,146
1998:
Saving Private Ryan $216,540,909
Armageddon $201,578,182
<p
>There's Something About Mary $176,484,651
Doctor Dolittle $144,156,605
Deep Impact $140,464,664
1999:
Star Wars: Episode I -- The Phantom Menace $431,088,301
The Sixth Sense $293,506,292
Austin Powers: The Spy Who Shagged Me $206,040,086
Tarzan $171,091,819
Big Daddy $163,479,795
2000:
Mission: Impossible II $215,409,889
Gladiator $187,705,427
The Perfect Storm $182,618,434
X-Men $157,299,717
Scary Movie $157,019,771
2001
Shrek $267,665,011
Rush Hour 2 $226,164,286
The Mummy Returns $202,019,785
Pearl Harbor $198,542,554
Jurassic Park III $181,171,875
2002
Spider-Man $403,706,375
Star Wars: Episode II -- Attack of the Clones $302,191,252
Signs $227,966,634
Austin Powers in Goldmember $213,307,889
Men in Black II $190,418,803

2003
Finding Nemo $339,714,978
Pirates of the Caribbean: The Curse of the Black Pearl $305,413,918
The Matrix Reloaded $281,576,461
Bruce Almighty $242,829,261
X2: X-Men United $214,949,694
2004
Shrek 2 $441,226,247
Spider-Man 2 $373,585,825
Harry Potter and the Prisoner of Azkaban $249,541,069
The Day After Tomorrow $186,740,799
The Bourne Supremacy $176,241,941
2005
Star Wars: Episode III -- Revenge of the Sith $380,270,577
War of the Worlds $234,280,354
Wedding Crashers $209,255,921
Charlie and the Chocolate Factory $206,459,076
Batman Begins $205,343,774
2006
Pirates of the Caribbean: Dead Man's Chest $423,315,812
Cars $244,082,982
X-Men: The Last Stand $234,362,462
The Da Vinci Code $217,536,138
Superman Returns $200,081,192
2007
Spider-Man 3 $336,530,303
Shrek the Third $322,719,944
Transformers $319,246,193
Pirates of the Caribbean: At World's End $309,420,425
Harry Potter and the Order of the Phoenix $292,004,738
2008
The Dark Knight $533,345,358
Iron Man $318,412,101
Indiana Jones and the Kingdom of the Crystal Skull $317,101,119
Hancock $227,946,274
WALL-E $223,808,164
2009
Transformers: Revenge of the Fallen $402,111,870
Harry Potter and the Half-Blood Prince $301,959,197
The Hangover $277,322,503
Up $293,004,164
Star Trek $257,730,019
2010
Toy Story 3 $415,004,880
Iron Man 2 $312,433,331
The Twilight Saga: Eclipse $300,531,751
Inception $292,576,195
Despicable Me $251,513,985