Transcript: As was first seen nearly a hundred years ago, when luminosities and effective temperatures are gathered for hundreds of stars near the Sun, the result is not a scatter plot. Most stars in the H-R diagram lie on a diagonal line or track that runs from hot, luminous, and blue stars in the upper left corner down to cool, faint, and red stars in the lower right corner. Stars with these properties are called main sequence stars. The main sequence runs across the H-R diagram, and it represents all stars that get their energy from the fusion of hydrogen into helium.