On 26 April 1986, at 1:23 AM, reactor number four at the Chernobyl nuclear power station exploded. The radiation released was over a hundred times more than that of the atomic bombs dropped on Hiroshima and Nagasaki.
At Chernobyl.info, a site dedicated to the longterm consequences of the disaster, there's a list of commemoration activities planned around the world for April 26, 2006. The site also contains historic details, an extensive index of projects aiding survivors, and interviews with people who lived through the disaster.
A related NPR news item ran today: "Voices of Chernobyl': Survivors' Stories" by Melissa Block featured some incredibly moving personal accounts from survivors who lost friends, family, and all their worldy posessions: Link to archived audio.
There are plans to install a new, billion-dollar cover over the disaster site to more effectively contain the 200 tons of radioactive fuel still present. The structure will cost about a billion dollars, and is scheduled to be in place by 2009. More info here, and NPR also ran a story on this today with background from Warren Stern of the U.S. State Department: Link.
A "sarcophagus" — a steel and concrete shell built soon after the disaster to contain the radiation is increasingly unstable. Engineers plan to slide an enormous Quonset hut-shaped cover over a breached reactor to keep more radiation from reaching the atmosphere.
(image: Vladimir Repik/Reuters, 1986. "An aerial view of the fourth reactor of the Chernobyl nuclear power plant after its explosion.")