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Use the Planck function to derive the surface area of your stars and hence  their radii (be careful converting units!). For comparison, the Sun has a radius of $7 \times 10^8$ m. How do they compare?  \subsection{Advanced \subsection{{\color{blue} Advanced  Exercises} {\color{red} Problems}}  {\color{blue}  If you've got this far and still have time and energy left, consider a few of the following. following.}  \begin{itemize}