A human in a spacesuit (or indeed anywhere) generates about 100W of heat. In the vacuum of space, the only way for this energy to escape is through radiation. T

A human in a spacesuit (or indeed anywhere) generates about 100W of heat. In the vacuum of space, the only way for this energy to escape is through radiation. The amount an object radiates depends on its temperature, its surface area, and its 'emissivity', which is simply 1-reflectance. Back of the envelope, a human sized object (2 m^2) with an emissivity of 0.12 (polished aluminum), generating 100W, will stabilize at almost exactly 20C - room temperature. So, you don't need the sun at all! Make your spacesuit small and shiny and you can enjoy balmy temperatures deep in the inky blackness of the interstellar void, for as long as your food and oxygen lasts (food and oxygen ultimately being the fuel for your 100W). Citations: https://en.wikipedia.org/wiki/Thermal_radiation https://en.wikipedia.org/wiki/Thermal_radiation and typing '100 Watt = 0.12 × (5.6704W⋅(10^−8)/(m^2⋅K^4)) × 2 m^2 × x^4 to celsius' into Qalculate