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Bob Berman's strange universe: Center of the action

April 2006: When ancient Greeks figured out Earth's a sphere, a new issue arose. Every ball has an "inside." Well, what's inside Earth?
Until the 20th century, astronomers were strictly outsiders. They ignored star and planet interiors. They had to. Telescopes showed only the tops of things. Scientists knew that a ball's "inside" constitutes virtually all its mass, and the limitation was frustrating. Basic questions went unanswered. For example, what lies below the dazzling solar surface? How can the Sun keep shining when even the highest-quality Sun-size lump of coal would burn itself out in 2,000 years? Observers suspected that fascinating, critical processes — and maybe life itself — might not hang out where it's convenient for us to view — like on surfaces. Of course, this frustration began long before the telescope.

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