Among the countries not invited is Iran, which the Unites States believes may be trying to make a nuclear weapon, despite frequent claims to the contrary.
A curtain raises to reveal a grand orchestra in Tehran - part of a full schedule of events to mark "National Nuclear Day." Only in Iran does uranium enrichment merit this level of pomp and ceremony, CBS News correspondent Elizabeth Palmer reports from the capital city.
It was a day, declared by President Mahmoud Ahmadinejad, for the country to feel proud of its achievements.
While Ahmadinejad urges Iranians to celebrate the country's nuclear program, the rest of the world is coming together under U.S. leadership to condemn it - and to press for tough aimed at halting it.
Iran's political leaders scoff at the idea.
But the head of the country's nuclear agency, Ali Akbar Salehi, who earned his Ph.D. at MIT in Boston, made a candid admission in a rare interview with CBS News.
"Of course sanctions will affect us," he said. "But it only will delay our projects. It will not stop our projects."
"They will hurt," he added. "Then we will have to come up with our own manufacturing systems."
Full Transcript of the Salehi Interview
Iran already uses homemade technology to enrich uranium in one plant, and recently announced it would build six more.
Tehran says it just wants to create fuel for nuclear power stations, but the U.S. suspects a secret plan to make a bomb.
Asked if the country is trying to make any kind of weapon, Salehi was unequivocal.
"No," he said. "We have indicated this many times. Not me, our president, our supreme leader. It's against our tenets. It's against our religion."
The U.S. and its allies might have more faith in that argument if Iran didn't do things like publicly unveil a new centrifuge that can enrich more uranium even faster, or make incendiary comments, like even Salehi sometimes does.
"Any military encounter with Iran will create consequences that are beyond anyone's imagination," he said. "It can put the entire region on fire."
Those are tactics that erode Western confidence in Iran - but please the crowds at home.