If the Sun expands to a radius of $100 R_{\odot}$ during the red giant phase, by what factor has its volume increased from its main sequence radius of $1 R_{\odot}$?

Answer

Approximately one million times ($100^3$)

The calculation for the volume change of a spherical object is proportional to the cube of its radius ($V ilde{} R^3$). If the initial radius is $1 R_{\odot}$ and the final radius reaches $100 R_{\odot}$, the volumetric expansion is calculated by cubing the radius ratio: $100^3$. This results in an enormous increase in volume by a factor of one million. This substantial increase in volume is not due to a corresponding increase in mass, but rather is driven by the tremendous puffing up and expansion of the star's outer layers, powered by the efficient shell fusion process deep inside.

If the Sun expands to a radius of $100 R_{\odot}$ during the red giant phase, by what factor has its volume increased from its main sequence radius of $1 R_{\odot}$?
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