A presidential birthday is a storied affair: Lincoln reportedly never celebrated them in office, but Reagan's surprise party in 1981 featured a dozen cakes, plus veal and lobster. Franklin Roosevelt received more than 100,000 birthday telegrams in 1934.

But no birthday compares to the big 5-0, and today President Obama (a Leo, natch) joins a group of only seven presidents who have celebrated that milestone birthday in office. Of those, he's only the third to do it in the past 100 years. In 1908, Teddy Roosevelt (whose ascent to the highest office was accidental, hastened in part by the assassination of his predecessor William McKinley) kept his birthday a "low-key affair."

Most of us remember the images from Bill Clinton's more extravagant party in 1996, with a teenage Chelsea helping her dad blow out seemingly endless candles, but nothing can compare to Marilyn Monroe crooning "Happy Birthday Mr. President," to her (alleged) lover JFK in 1962. But that wasn't Kennedy's 50th birthday— just his 45th.

So will Obama's birthday be a big deal or fly under the radar? He's already made a trip to Chicago for a public concert by Jennifer Hudson (who led the crowd in "Happy Birthday"), Herbie Hancock and OK Go, and a well-heeled Wednesday night fundraiser dinner that raised $3.6 million for the Democratic National Committee.

As for the president's Thursday, he has meetings scheduled for the morning, followed by a private birthday party at the White House with a few friends flying in from Chicago and 14-year-old Malia Obama making a special appearance from summer camp. The real relaxation doesn't begin until the weekend, when the president and his family will be taking off to Camp David, and perhaps later in the month when the Obamas vacation in Martha's Vineyard.

A handful of events and a serenade by an Oscar winner would be a banner birthday in every other regard, but the scarcity of big functions is likely due to worries over seeming out of touch when the economy is still in a rut — the Obamas are personally paying for the White House party — and also because of the legitimate concern that the agreement to raise the debt limit might not have fallen into place before the president's birthday.

Obama said a debt limit agreement was on his birthday list, but after the tough weeks of debate and an unpopular solution, it might not feel like much of a gift. Certainly nothing like the one Harry Truman got in 1945 — the surrender of Germany in World War II.