Hydrogen is the first element on the periodic table of elements. It is a colorless, odorless gas, and is denoted by the atomic symbol H. It has an atomic number of 1 and an atomic weight of 1.0079.

Hydrogen is the source of most of the energy radiated by the sun and other stars. The enormous amount of heat and light that we get from the sun comes from hydrogen-fueled reactions. When we burn oil or other fossil fuels, we are actually using the sun's energy, which was stored millions of years ago by ancient plants.

Hydrogen is remarkable in many other ways as well. Its atom is the lightest, smallest, simplest atomic structure known, consisting of just a single proton and single electron (these are subatomic particles with positive and negative electrical charges, respectively). Yet these minuscule hydrogen atoms make up 90 percent of all matter in the universe. On...