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.
If Star A is twice as far from Earth as Star B but they still BOTH appear to have the same amount of brightness, then if we compared the stars at the same distance from the Earth, Star A would be brighter. So Star A will have the greater absolute brightness.