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.
In this way, you can actually figure out how the relative brightness of a star compares to another if you know their magnitudes. Just use the equation on your screen to do this. Here b stands for the apparent brightness of a specific star and m stands for the magnitude of a star.