 
All the stuff in the universe is made of matter, but we are only familiar with it being a solid, liquid, or gas. However, there is a fourth state of matter, called plasma.
In a solid, the molecules, comprised of atoms, are held together in rigid structures. The molecules can vibrate, but can't move relative to one another. In a liquid, the molecules are less tightly bound, and have enough energy to slide around relative to each other, but can't escape the liquid structure. In a gas, the molecules have acquired enough energy to escape the force of attraction of the other molecules, and are free to move wherever they want without constraint. Plasma is the fourth state of matter. Heating any gas to a high enough temperature will cause the electrons in atoms to be stripped away from their associated nuclei, in a process called ionization. At temperatures in the tens of thousands of degrees, even the atoms will eventually come apart, and the hot gas becomes a sea of electrons, protons and neutrons, called a plasma.  
The sun, like most stars, is almost entirely plasma, making plasma the most abundant state of matter, comprising over 99% of the visible universe. In northern skies, auroras are plasmas made up of ionized oxygen atoms, with energy having come from solar storms. Lightning is a plasma made from molecules of air ripped apart by elecrical charges. |