This suggests a possibility to try. Maybe all stars are the size of the Sun, but the hotter ones are more luminous just because they are hotter. We can test this with the HR diagram:
Our hypothesis would be that all main sequence stars fall on the blue line.
Here is the comparison:
Our idea was wrong. But we learned something. The coolest main sequence stars are a lot smaller than the sun. The hottest main sequence stars are a lot bigger than the sun.
Davison E. Soper, Institute of Theoretical Science, University of Oregon, Eugene OR 97403 USA email@example.com