# 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?

##### 1 Answer

May 27, 2018

The star's radius is 9 times our Sun's radius

#### Explanation:

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

So

Which means:

For spherical bodies:

The star's radius is 9 times our Sun's