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.
Polaris or Alpha Ursae Minoris (Alp UMi) is the brightest naked eye star in the constellation Ursa Minor. With an apparent magnitude of 1.97v, Polaris is the 46th brightest star in the entire sky (see: 50 Brightest Stars). Its absolute magnitude is -3.64 and its distance is 431 light years.