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.
That line is the main sequence (of course, you must plot the absolute brightness â or luminosity â not the apparent brightness; do you know why?). Hertzsprung-Russell Diagram. Credit: ESO. As you might have expected, the discovery of the main sequence had to wait until the distances to at least a few hundred stars could be reasonably well estimated (so their absolute magnitudes, or luminosities, could be worked out).