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.
Figure 4. A different view of the star tetrahedron. There are 4 axes of rotation for the star tetrahedron; AB, CF, DE, and GH. Notice the planes CGE in green and HDF in purple; both planes go into and out of the screen or page.