Imagine the Universe!
Imagine Home  |   Ask an Astrophysicist  |  
Ask an Astrophysicist

The Question

(Submitted March 01, 1998)

All I wanted to ask you is that if we put a thermometer in Space with no other light or heat source around and absolutely no background radiation there, what would it read? Would the temperature be really cold or what?

The Answer

Yes, it would be really cold. Temperature measures the energy per "degree of freedom" (i.e. way something can move) of whatever molecules happen to be around. So, it it becomes so cold that the molecules stop all together, then this is the "absolute zero" temperature. On the Celsius Temperature Scale (i.e. water freezes at 0, and boils at 100) this takes place at -273 degrees C.

We usually use the Kelvin temperature scale, where Zero Kelvin is this "absolute zero" temperature -- or -273 degrees C. Water freezes at +273 Kelvin and water boils at +373 Kelvin.

If we put a thermometer in darkest space, with absolutely nothing around, it would first have to cool off. This might take a very very long time. Once it cooled off, it would read 2.7 Kelvin. This is because of the "3 degree microwave background radiation." No matter where you go, you cannot escape it -- it is always there.

Jonathan Keohane
for Ask an Astrophysicist

Previous question
Prev
Main topic
Main
Next question
Next

If words seem to be missing from the articles, please read this.

Imagine the Universe! is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Project Leader: Dr. Barbara Mattson
Curator: Meredith Gibb
Responsible NASA Official: Phil Newman
All material on this site has been created and updated between 1997-2014.
This page last updated: Thursday, 01-Dec-2005 13:58:40 EST