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.
The Hertzsprung - Russell Diagram. 1  Objective: 2  Apparent (Visual) and Absolute Magnitude. 3  Apparent magnitude, m, is the relative brightness of a star (or other stellar object) as viewed from the Earth; the lower the magnitude, the brighter the star.