These subtleties are important when building a nuclear bomb or nuclear power generator. For a bomb one has to get enough fissionable material to initiate a runaway chain reaction. For a power plant a steady-state must be maintained to prevent a runaway reaction (melt down). How?

Mssr. Messier was a self-educated astronomer until he began working for the French navy in 1751. Six years later he began searching for Comet Halley, which was predicted to return in 1758. His independent recovery of that famous object in early 1759 launched his career as a comet hunter, but he...

What does Mars tell us about the potential for habitable environments on other planets with masses different than that of Earth? Mars already has indicated that important geologic processes such as volcanism decline more rapidly on smaller planets than on Earth, leading perhaps to the more rapid...