"First Lightning," a 22-kiloton nuclear bomb, exploded at 7 a.m. local time on August 29, 1949, at the Semipalatinsk testing site in northern Kazakhstan.
The Cold War nuclear arms race between the Soviet Union and the United States had begun. The United States, which had already demonstrated its nuclear capability with the deadly twin bombings of Hiroshima and Nagasaki in 1945, dubbed the Soviet test bomb "Joe 1," after Josef Stalin.
At the time, the explosion was a source of pride for the people of the Soviet Union. But that blast, and the hundreds that followed it at the 18,000-square-kilometer site at Semipalatinsk, left a legacy of misery for the people living there.
By the time it was finally closed in 1989, the Kazakh base -- which had been selected by Lavrenty Beria, the infamous head of the NKVD secret police -- had been the site of 456 atmospheric and underground nuclear tests, nearly one-quarter of all the nuclear tests ever conducted in the world.
The "First Lighting" test was hailed as a success. Amid the celebrations, few noticed that Beria's claim that the Semipalatinsk region was uninhabited was wrong.
Nor did the issue gain much attention as tests continued over the next four decades. In fact, some of the people of northern Kazakhstan were unwittingly turned into experimental subjects. Residents were ordered to step outside their homes during test blasts, so that they could later be examined as part of studies on the effects of radiation.
Zoya Mikhailovna is a resident of the Kazakh city of Kurchatov, named after Soviet scientist Igor Kurchatov, who headed the Soviet Union's nuclear development program.
The city was the center for the scientists that developed the Soviet Union's nuclear weapons in the early days of the Cold War. Mikhailovna retold her mother's stories about the nuclear tests for RFE/RL's Kazakh Service.
"According to my mother's stories, military forces used to ask all the residents to leave their houses, and one could see smoke like a mushroom in the skies after an explosion," Mikhailovna said. "I used to feel earthquakes when I was sleeping. When we felt the earthquake, we knew that there had been an explosion. Later we got used to it. Then the authorities started exploding those bombs without any warnings at all."
Thousands of cases of birth defects, cancer, and neurological illnesses have since been reported in the Semipalatinsk region. Livestock living within range of the site also suffer from deformities and other defects.
Zhanbolat Gilmanov is an employee at Kazakhstan's National Nuclear Center, which currently focuses its work on the uranium industry and the nuclear energy industry. He said Soviet authorities distorted the truth about the power of the bombs being tested.
"Certain information was far from reality in those days. For example, the media reported that a 20-kiloton atomic bomb had been detonated as the Semipalatinsk site. However, when we investigated and measured the bomb's power, we would find out that it was actually 80 kilotons," Gilmanov said.
"The authorities used to report the size of any bomb detonated at the site as being as small as possible. Therefore, all those figures from 0 to 20 kilotons mentioned in some books were false information," he added.
Gilmanov said these exaggerated figures left people unprepared for the consequences.
"From the human viewpoint, this was the wrong thing to do, because these explosions brought not only economic losses for people but also huge moral damage. The environment was badly affected, the land became useless," Gilmanov said. "There is no such nuclear testing site in other countries -- not in the United States, France, or China. Out of 715 [Soviet] nuclear bombs, 500 were tested in Kazakhstan. The reason for this isn't clear."
And as Dmitry Kalmykov of the Ecomuseum in Semipalatinsk told RFE/RL's Russian Service, the consequences of those tests can still be seen today -- and likely for many tomorrows to come -- because the area is still inhabited.
"The Semipalatinsk testing site is the only test site in the world [where people live], and the Kazakh people are the only people in the world who live on a [nuclear] test site," Kalmykov said. "The civilian population, as they have for years, continue to live on the testing site. In my opinion this is the major problem."
How many people live in the contaminated area remains unclear, although Kalmykov said it may be as many as several thousand.
Most nuclear testing sites are in remote areas -- the Nevada desert in the United States, or lonely atolls in the South Pacific for French tests. Such areas are clearly marked as hazardous to human health.
Kalmykov said that contributing to the problem in Kazakhstan is the fact that no one in Semipalatinsk is sure where the contaminated areas are.
"These people [living in the area] don't even know exactly where the testing site is. We conducted a poll among the police, doctors, employees of the governor's office. They don't know if they are living on the test site, or next to it," Kalmykov said.
"In general, I could go on for half an hour talking about what they don't have and don't know. There is practically no information about protection [from radiation exposure] from the government."
Kazakhstan's government has at various times said it would resettle people living in Semipalatinsk "dead zones" or fund the cleanup of designated areas in the region. But there is little evidence that officials are carrying through with such plans.
The Kazakh media occasionally features feel-good stories about individual victims of the tests who receive special medical treatment abroad, such as Berik Syzdykov, a Kazakh man who was born horribly deformed and has undergone radical plastic surgery paid for by various foreign charitable organizations.
There is also the Nevada-Semipalatinsk Movement that was organized in the late 1980s, during Soviet leader Mikhail Gorbachev's perestroika period. It united concerned citizens in Kazakhstan and the United States to press for a cessation of nuclear testing. The movement was a respected example of grassroots detente. Testing stopped at Semipalatinsk in 1989, and Kazakh President Nursultan Nazarbaev declared the site closed in 1991.
The Central Asian presidents chose Semipalatinsk as the site for the signing in 2006 of a multilateral declaration on keeping the region nuclear-free.
But the August 29 anniversary of the first test is more likely to be a day of mourning for the people still living on and near the Semipalatinsk site.
No one can say for sure when, or even if, the area will be safe to live in again.
RFE/RL Kazakh Service director Yedige Magauin and Yermek Boltaev of the Kazakh Bureau, and Irina Lagunina and Malika Rakhmonova of RFE/RLs Russian Service all contributed to this report.