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.
a. the brightness of a celestial body as expressed on a logarithmic scale where an increase of 1 equals a reduction in brightness by a factor of 2.512, the sixth magnitude being the dimmest observable with the naked eye. b. absolute magnitude.