Fifty years ago, the world's first atomic explosion shattered the desert dawn in New Mexico, just an hour's drive from a town called Truth or Consequences. The date was July 16, 1945.

The world has never been the same.

At first, an official smoke screen surrounded that nuclear detonation; code-named ''Trinity,'' it was part of the super-secret Manhattan Project.

The government's cover story moved on the wires of Associated Press: ''An ammunition magazine, containing high-explosives and pyrotechnics, exploded early today in a remote area of the Alamogordo air base reservation, producing a brilliant flash and blast which were reported to have been observed as far away as Gallup, 235 miles northwest.''

But three weeks later, when a U.S. plane dropped an atomic bomb on Hiroshima, humanity learned that it had gained the ability to destroy itself.

The unfathomable power of a single warhead shook a routine assumption: that despite the mortality of each individual, the human race would endure. The image of a mushroom cloud evoked unprecedented horror. Yet, nuclear weapons quickly became part of America's political, cultural and economic landscape.

By July 1946 -- when the United States began peacetime testing of A-bombs in the Pacific -- the media spin had settled into nuclear boosterism. Newsweek provided advance coverage under headlines like ''Atomic Bomb: Greatest Show on Earth'' and ''Significance: The Good That May Come From the Tests at Bikini.''

Forty-two thousand U.S. military personnel were within a few miles of the first two explosions at the Bikini atolls. The American press downplayed the bomb's impact. ''Awful as it was,'' Time magazine reported, ''it was less than the expectations of many onlookers.''

During the next 16 years, more than 200 mushroom clouds rose over test sites in the Pacific Ocean and the Nevada desert. The fallout ravaged the health of downwind residents from the Marshall Islands to Utah, Nevada and northern sections of Arizona.

Opponents of nuclear tests didn't get much ink or air time in the 1950s -- while baby boomers grew up with radioactive isotopes in their bodies, courtesy of American and Soviet nuclear tests spewing fallout to the global winds.

The 1963 Limited Test Ban treaty pushed tests underground. It was a major victory for public health. But bomb testing -- and the nuclear arms race -- continued out of sight and out of public mind.

Beginning in the late 1970s, some of the 300,000 U.S. veterans who had been exposed to above-ground nuclear tests at close range -- ''atomic veterans'' -- stepped forward to talk about unusually high rates of cancer as well as birth defects among their children. Similar evidence has come from nuclear industry workers and people living downwind and down river of nuclear facilities.

In 1988, a major scandal rocked the Department of Energy, the federal agency in charge of atomic weapons plants emitting extensive radioactive pollution. But rather than widening debate over nuclear arms policy options, the media focus was narrow: How could the country clean up and modernize its weapons assembly line?

These days, with bipartisan support, the White House is implementing new multibillion-dollar programs to ''upgrade'' the nation's nuclear weapons labs.

Meanwhile, although news media hardly seem to notice, some voices keep insisting that it's wrong to build nuclear weapons. One of those voices belongs to Samuel H. Day Jr. of Madison.

After a journalistic career -- including jobs as an AP reporter, editor of the Bulletin of the Atomic Scientists and managing editor of The Progressive magazine -- Sam Day found that he could no longer just write news and commentary.

Today, at age 68, Day is in prison. He's serving a six-month sentence for stepping onto the grounds of the U.S. Strategic Nuclear Command headquarters in Nebraska to protest nuclear weapons.

A federal court in Omaha declared Sam Day to be a criminal. But Day pointed out that grave criminality could be seen in the highest offices of the land: ''Under international law, it is a crime to point weapons of mass destruction at defenseless cities. Under international law, it is the duty of every citizen to do everything possible to prevent such crimes.''

The nation's military command, he added, ''controls the targeting and launching of many thousands of nuclear warheads, some more than 100 times more powerful than the bomb that destroyed Hiroshima.

And I chose to come here now because, contrary to public opinion and despite the end of the Cold War, our government has not relinquished one iota of its capacity for waging nuclear war. And it has no intention of doing so.''

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