That’s the cornerstone of the 2009 national promotional campaign, “What will you celebrate?” announced today by Walt Disney Parks and Resorts. Anyone showing up with a valid ID including proof of birthdate will get a free ticket on that day in 2009 for one of the theme parks at Disney World or at Disneyland in California.

Disney officials announced the promotion as their effort to cash in on what they described as a growing trend called “celebration vacations” — trips to vacation spots that people take to celebrate big birthdays, big anniversaries, honeymoons and other momentous personal occasions.

Disney World probably already gets a lions’ share of such vacations, according to a Ypartnership marketing survey that Disney commissioned. But until now the company has never put together a unified marketing campaign to attract such celebrations on a large scale.

Even though a free ticket — essentially $75 discount — might seem almost insignificant in a family vacation budget that might run several thousand dollars, Disney’s goal is to get more people at least considering bringing their birthdays to Disney World.

The promotion also will give Disney a new tool to help assure that its theme-park turnstiles keep moving in the next year even if the teetering national economy starts dragging down the tourism business.

While the promotion was announced in New York City, with the aim of attracting national and international visitors, Central Floridians may cash in most easily and most often.

“We not only open up the opportunity, we hope they’ll take the opportunity, ” said Jay Rasulo, chairman of Walt Disney Parks and Resorts. “The flip side of that is, nobody celebrates their birthday by themselves. They bring their family, their friends and their kids with them.”