Q&A: General Astronomy and Space Science

Q:
What is "molecular gas"? How is it different from regular gas?

A:
A molecule is a closely knit group of two or more atoms that are bound together by electromagnetic forces among the atoms. Molecular gas, therefore, is made up of molecules in a gaseous phase of matter, where the molecules are far apart and can move around freely. One of the most familiar and important of all gases is the Earth's atmosphere, which is dominated by molecular gas, such as nitrogen and oxygen. So, in an important sense this is "regular gas". Outside the earth's atmosphere you can find a wide range of gases ranging from extremely hot, highly ionised gas to very cool molecular gas.