This is CBS I In The World. I'm John Batsuit, Dr. Ken Croswell.

His new piece at Sky and Telescope, The July Issue, is about red supergiants, which

itself is a critical understanding of all the stars in the heavens, of their lives,

of their billions of years' lives, or hundreds of millions of years' lives.

In 1929, Edwin Hubble discovered the age of the universe because it's expanding, and

the expansion and the age were critical to understand, because now stars didn't have

trillions of years to evolve. They had to do it within what they understood was the timeline

of everything. How did that help understanding the main sequence, Ken?

Professor Eddington, as we had been discussing, had raised problems for Henry Norse's

theory of sterile evolution, but he also suggested a way out. He suggested that if the universe

was trillions of years old, then the stars could gradually consume their mass, as they

shown. That would explain why the blue dwarfs were more massive than the yellow dwarfs,

and why the yellow dwarfs were more massive than the red dwarfs. But in order for that

to work, the universe had to be trillions of years old. That was Eddington's idea that

maybe the stars simply slowly burned their mass over time, and got smaller. That would

explain the mass-luminosity relationship that he had discovered in 1924. But when Edwin

Hubble discovered that the universe is expanded, and by backtracking that expansion concluded

that other stars concluded that the universe was only billions of years old, not trillions

of years old, well, that Eddington option became not viable anymore. As a result, the whole

subject of solar evolution was really thrown into confusion. In fact, I have a quote from

an astronomer at the University of Michigan, Dean McLaughlin, who wrote, for several years,

I have told students that I knew all about solar evolution in 1923, less in 1925, and nothing

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