In Under Alien Skies, Dr. Philip Plait takes readers on a tour of the universe, including discussing what it might be like to live on planets in a variety of different star systems. A major factor to consider for this thought exercise is the mass of the star or stars involved, and what point they are at in their life cycles.

Stars are formed out of nebulae, huge clouds of dust and gas drifting in space. When areas of these clouds become dense enough, gravity will begin to pull them together. Once this process has begun, large clumps of raw material will condense. The center of these clumps heats up, forming protostars, while material that develops an orbit around them without being drawn in may eventually become a planet or other astronomical object.

If the protostar has enough mass, eventually its core will heat up enough for the fusion of hydrogen into helium to occur, at which point it becomes a main sequence star. Stars are classified based on their surface temperature, ...