astronomy college level

Question

Based on the Inverse Square Law, what is the brightness ratio for Sirius?

1:16

16:1

any of these

1/16

Answer 1

At a distance of 2.5 pc for Sirius, I assume the brightness ratio is comparing actual brightness to brightness at 10 pc. At 10 pc it would be 16 times fainter. But your wording does not specify what ratio is requested.