# How close to the sun would a spacecraft have to go to reach the distance at which the flux of solar energy is 20 times as large as the solar energy flux at the earth?

##### 1 Answer

.22 AU

#### Explanation:

The total amount of energy that that a star gives off is called the luminosity of the star. Luminosity cannot be measured directly for a star, however astronomers can measure how much energy is received from a star over a given area. That quantity is flux. Flux and luminosity are related by the formula;

Where

We can find the distance by setting the ratio of fluxes equal to

Rearranging the terms we get;

The distance between the Earth and the sun is defined to be 1 astronomical unit, so we can use this distance as