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.
Apparent magnitudes and absolute magnitudes. The brightness of a star of a given luminosity L, radiated in all directions, falls off as one over the distance to the object squared:, that is b(D) is proportional to L / D2. Objects of the same luminosity that are located at different distances from us will have different apparent magnitudes.