Radiation 101: What is it, how much is dangerous, and how does Fukushima compare to Chernobyl?

Our last blog post about Chernobyl generated a lot of interest among our friends, but seemed to raise more questions than it answered. Many people asked for more basic information about radiation and more comparisons between Chernobyl and Japan, and safe levels versus dangerous levels. In light of that, we have compiled this follow-up post.