The Hertzsprung-Russell diagram
"Wart on the Umpire's Nose"

The Hertzsprung-Russell diagram is the bulwark of stellar evolution, but consider this little story:
An umpire is standing in a crowded stadium. Upon his nose is an intelligent wart. This wart desires to know the process of evolution of its host, the umpire. To aid itself in this quest, the wart observes the other people in the stadium. Although the wart cannot see, it is able to monitor the heartbeats and blood pressure of the people present. Armed with this information, the wart constructs  a graph upon which it now places its data.

The Hertzsprung-Russell Diagram, where luminosity is replaced with blood pressure, and temperature with heartbeat.

The wart now mistakenly believes that by comparing people in this manner it has acquired a system that displays a sequence of evolution birth to death. The graph displays no such information; it merely describes the momentary state of excitement of the people in the stadium.

Published in Science News, Vol. 177, Mat 17th, 1980