In astrophysics, the Sun acts as a controlled, local laboratory for understanding other stars, best described as what metaphor?

Answer

A Rosetta Stone

The relationship between our star and others allows scientists to test models, making the Sun serve as a controlled, local laboratory—a Rosetta Stone—for understanding the physics driving all other luminous bodies.

In astrophysics, the Sun acts as a controlled, local laboratory for understanding other stars, best described as what metaphor?
sunastronomystarcelestial body