Final answer:
The H-R diagram shows the Sun's luminosity as 1, which is used as a standard for comparing the luminosity of other stars.
Step-by-step explanation:
The Hertzsprung-Russell diagram, or H-R diagram, is used to compare and understand the luminosity and surface temperature of stars, with a common reference point being our Sun. On the H-R diagram, the Sun is situated on the main sequence—a diagonal band running from high temperature, high luminosity stars in the upper left, to low temperature, low luminosity stars in the lower right. The Sun's position corresponds to a luminosity of 1, as it is the standard by which other stars' luminosities are compared.