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.
A luminance histogram is a bar graph. The x axis (the bottom line) shows brightness levels in a range starting at zero (pure black) on the left and finishing at 255 (pure white) on the right.