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.
Astronomy is an enormous subject. Only a selection of glossary is included mainly to help those who are new to astronomy to understand the subject published in this web site. absolute brightness-The apparent brightness an object would have if it were placed at a distance of 10 parsecs (33 light years) from Earth.