Concrete is the most common artificial composite material of all and typically consists of loose stones (aggregate) held with a matrix of cement. Concrete is a very robust material, much more robust than cement, and will not compress or shatter even under quite a large compressive force.
2) Y-axis contains absolute brightness Why do astronomers use the H-R Diagram? Astronomers use H-R Diagrams to classify stars and to understand how stars change over time.
Main Sequence on the Hertzsprung-Russell Diagram. About 90% of the known stars lie on the Main Sequence and have luminosities which approximately follow the mass-luminosity relationship. The Hertzsprung-Russell Diagram is a plot of luminosity vs temperature, except that the temperature is decreasing to the right on the horizontal axis.