Q&A: General Astronomy and Space Science
What is "molecular gas"? How is it different from regular gas?
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.