Late June (29th or 30th, I don't remember), 1908, in the middle of Siberia something exploded with a force in the 20 kiloton range. The rattle was picked up on seismic instruments in the UK, and the difussion of light through atmospheric particulates was such that there was no night in northern Europe for two or three days. No ground crater, it was an airbursting whatever it was.

There are a couple of theories. My personal favorite is that it was a baby comet that blew due to air friction; the meteor theory parallels it but it would have to be a stony meteor becuase the Soviets got nothing on MAD sensors when they did an aerial survey in the 50s. Others theories that are almost possible but rather doubtful include a really tiny peice of antimatter, say about 20 times the size of what we have in the vault at fermilab, or micro singularity, a pin head blackhole. (Both would explain why some reindeer had what appear to be rad burns, but there is some mathematical evidence that any blast that big will have some radiation.) Going down the scale of oddness, you have the possiblity that a meteorite of something that could be compressed until it reached critical mass did a grav dive before cooking off.

Then there is a peice of actually halfway decent science fiction from the late 40s, early 50s from a professor in the Soviet Union who suggested that it was the powerpack on a UFO going critical. Honestly, if I had to ride a busted ship down to Earth in northern summer, I might steer for Siberia myself, bail out, hit the PLB and wait for my version of a Pave Low to show up. It's still one of those places you reach by going to the middle of nowhere and keep going for a few days. But honestly, if you can build a starship, you probably have fusion reactors, not fission. Fusion bottles aren't likely to be able to go off like that- you let the heat out and the reaction will stop, it will just be a splash of star-hot plasma that will take care of everything for a ways.

The reason why I asked if anyone here was going to or knew of plans to celebrate is becuase it is a little killer lump of something from space. And lets face it, if had happened over a Warsaw Pact or NATO nation in the 50s, the internet would have been invented by a cockroach. :P It is a little bit TEOTWAWKI, but it's also kinda cool. As a group we are odd enough that someone might celebrate it. Other than me.