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.
North is down, and the scale around the edges is in seconds of arc. The dot-dash line is the orbit's major axis. The orbital plane is tilted to the line of sight by 25 degrees, so that Castor A does not appear at the focus of the orbit (where it actually is). The period is so long that we have yet to see the stars make a full turn around each other. Each of the two is again double. Castor C lies 1.2 minutes of arc away.