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.
Mars' brightness will match the star Sirius, which is the brightest of all the stars. The planet will be in the constellation Virgo, 6 degrees north/north-east of the bright star Spica. As a coincidence, on the same night that Mars is closest to Earth, you can see a total lunar eclipse.