We often refer to infrared radiation as being primarily heat (or thermal) radiation. But what
exactly is heat, and how does it differ from temperature? Simply put, heat is a measurementof energy. All molecules contain some amount of kinetic energy, that is to say, they have some intrinsic motion. The hotter an object is, the faster the motion of the molecules inside it. Thus, the heat of an object is the total energy of all the molecular motion inside that object.

Temperature, on the other hand, is a measure of the average heat or thermal energy of the
molecules in a substance. When we say an object has a temperature of 100 degrees C, for
example, we do not mean that every single molecule has that exact thermal energy. In any
substance, molecules are moving with a range of energies, and interacting with each other
as well, which changes their energies. But if we average the thermal energies of all the molecules together, we can obtain an object’s temperature.

How cold can it get on Earth? How hot can hot truly get?  These are important questions, and to find out the answers, here is the ultimate thermometer which takes you from absolute zero to what scientists think is the absolute heat limit.

Click the infographic to see a larger, more legible version:

The coldest of cold and the hottest of hot (temperatures, that is)

Sources:  NASA and BBC