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.
Apparent Magnitude The apparent magnitude of a celestial object, such as a star or galaxy, is the brightness measured by an observer at a specific distance from the object. The smaller the distance between the observer and object, the greater the apparent brightness. (left) Two stars, A and B, with the same apparent magnitude. (right) However, star A is actually a more luminous star that is further away from the Earth than than star B.