Is space cold? (and why the 20 char min for a question post?)

Question

If so... why is it so hot (265 deg F) on the daylight side of the moon?

If not... why were the apollo 13 astronauts nearly frozen on their return trip to earth?

Answer 1

Oh boy, very simple question, very difficult explanation.

Temperature is vibrating molecules. You detect heat when a molecule bounces into your skin. More molecules and harder bouncing means more heat. But there are three ways of transferring heat, two of which are imporant. One if by the (air) molecules vibrating and bouncing into eachother, the other is by radiation. When you hold your hand over a fire, the heat you feel is from the vibrating molecules hitting your hand. When you hold your hand near a lightbulb, you're feeling the radiotion heat your hand.

Lets say you take a thermometer and put it in space, on the night side of the earth. Now, because there is no air in space, no molecules to vibrate, the thermometer will cool down, to almost absolute zero. It will cool down slowly, because of the same lack of air, but more on that later.

But if you take that same thermometer and place it on the day side of earth, it will reach a very high temperature, because of the radiation of the sun hitting it. That radiation doesn't need molecules to heat the termometer.

It's like on earth, on a sunny day. When you're in the shade you feel warm because the air is warm, when you're in the sun, you feel the air as well as the radiation from the sun. Except that in space, there is no air.

Now, why is the moon so hot during the day? The "sand" on the moon is directly exposed to the rays from the sun. On earth, we have thousands of feet of air between us and the sun, but on the moon, there is nothing. That air heats up, absorbing a little of the sun's rays, and then a little more, and a little more, until you reach a comfortable temperature. On the moon, the sun shines directly down to the ground.

Wht did the astronauts almost freeze? Because they were in the shade all the time, and in space, the shade is extremely cold. The astronauts would have frozen much sooner if there was air though.

Because there is no air in space, heat can't be transferred by vibrating molecules, but neither can "cold be transferred". The only way for the apollo capusule to cool off, was be radiating it's heat away, which is, luckily for astronauts, a very slow proces.

I hope that was clear enough. If not, feel free to send a message.