Alight-year measures the that light travels in 1 year.

distance

Explanation:

Light year is a unit of measurement that is used for astronomical purposes only.  

Basically it is equivalent to the distance traveled by light in a time frame of one year.  

One light year is equal to km which is approximately equal to six million miles.  

In case of distant stars and planets where human have not yet reached or are not even aware of the distance at which they are,  light year is used as a distance measuring unit.  

the darker peppered moth species were favored due to the fact that the industrial revolution had made all the nearby trees a darker color instead of white.

thinking it would be physical characteristics