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.
Because apparent magnitude is the brightness of a star, as seen from Earth, whereas absolute magnitude is the brightness of a star as seen from the same distance-about 32.6 light years away.  Absolute magnitude is the brightness of an object as seen from a predete â¦ rmined distance, depending on the object.    For planets, the distance used is 1 AU (Astronomical Units). Stars and galaxies use 10 parsecs which is about 32.616 light years.