Therefore, Capella has 100 solar luminosities. A star's spectrum can be classified by its light's spectrum. Binary stars physically linked to one another by gravity are called visual binaries. Binary stars that are not actually linked to one another, but appear to be, are called optical binaries. Optical binaries occur when one star is closer to the Earth than another, but they appear from our perspective to be close to one another.
Stars range in density from very tenuous to very, very dense.
At that density, one cubic centimeter would weigh as much as a large truck. Stars are powered by a hydrogen-fusion reaction. When the raw fuel for this reaction runs out, its core contracts and heats up, causing the hydrogen fusion shell to ignite. This, in turn, causes the star to expand into a giant star. The contraction of the star's core may ignite the helium that is left there.