# Radiative equilibrium in near-Earth space

1. Apr 13, 2007

### nugae

Project a pig P from a spacecraft in near-Earth orbit. Assume that P is rotating rapidly (or, equivalently, that it is perfectly conductive).

What temperature will P reach when it is in radiative equilibrium with the Sun on the one hand and the CRB on the other?

The Stefan-Boltzmann law gives 278°K (at least according to Wikipedia) if the pig is a black body without an atmosphere, which seems reasonable though I haven't actually checked the calculations in detail.

This question may be turning into "how un-black is a pig?". Presumably one would need to look at the albedo of pigs (either black ones or white ones) at different wavelengths. Any references would be welcome: people might have more figures on them than pigs, and, both being mammals, will probably have similar radiative properties.

If a body absorbs 30% of the radiation that a black body would, will it also emit 30% of the radiation that a black body would, or is there no necessary connection between these figures?

2. Apr 13, 2007

### marcusl

The emissivity of most organic materials (skin, paper, etc.) is close to 1 in the infra-red. For human skin it's 0.95-0.98, regardless of skin color, dropping to about 0.9 in the near-IR.

Emissivity is reciprocal for absorbtion and radiation.

3. Apr 14, 2007

### cesiumfrog

If it didn't, would energy be conserved?