A star with the same color as the Sun is found to produces a luminosity 81 times larger. What is its radius compared to the Sun?
The star's radius is 9 times our Sun's radius
Luminosity, measured in energy delivered per unit time, is according to the Stefan–Boltzmann equation:
#L= sigma A T^4#
That black body colour is related directly to average temperature is summarised in Wien's Law:
# lambda_("max")=b/T #where #b#is another constant
For spherical bodies:
The star's radius is 9 times our Sun's