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.
Astronomers have figured out that an increase of 5 magnitudes is equal to a 100-fold decrease in brightness. Thus, an increase in one magnitude is equal to the fifth root of 100, which is 2.512. This means something like a fourth magnitude star is 2.512 times brighter than a fifth magnitude one.