system
Given the following post, respond as if you're commenting on Reddit:
human
Why was it so cold inside Apollo 13?

Seems to me it should have been too warm.  Space is not cold, it is a vacuum, a great insulator.  Add to that the full force of the sun on the capsule 24/7, and three adult bodies each creating their own heat in quite a small space.  The only way for the capsule to cool is radiation.  Why did it cool so effectively?
gpt
> Why did it cool so effectively?

Because it was designed for that.

You're right that space is a great insulator and that radiation is a very inefficient method *when compared to conduction and convection*, but it's not that hard to cool down. Radiated power grows with the fourth power of the temperature, and the capsule had a large outer surface area.

A spacecraft must calculated to radiate a power equal to the sum of absorbed sunlight, the heat generated by the occupants and heat generated by equipment. It was the third that was diminished when they lost power from a fuel cell and tried to save battery power as hard as they could by turning all equipment off.

Just some quick math, the command module was 11m long and 3.9 m wide, approximating this as a cylinder would be an external surface area of 135m^(2). It's not impossible to radiate a couple of kilowatts from such a big surface.