A star begins its "life" in a contracting
nebula of gas and dust. As the density of the material
increases under the influence of gravity, compression
heats the material. If the material gets hot enough,
hydrogen atoms begin fusing together to form helium
atoms, and a star is born. A star will spend most of
its life, called the main sequence phase, fusing
hydrogen into helium.
! Click the image to see the animation.