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.
Libra, the Scales. Libra represents a balance scale. The name may come from the fact that the Sun passed across the face of the constellation at the time of the autumnal equinox in September, when day and night are of roughly equal length, so the heavens are balanced.. Libra's brightest stars, however, are named for the next constellation over, Scorpius. The stars are Zubenelgenubi and Zubeneschamali, which are Arabic names that mean the southern and northern claws, respectively. In ancient times, the stars represented the scorpion's claws.