Final answer:
A light-year is a measurement of distance that light travels in one year, which is approximately 9.5 trillion kilometers, based on the constant speed of light being 300,000 kilometers per second.
Step-by-step explanation:
The term light-year is used by astronomers as a unit of distance. It defines the distance that light travels in one year. Since light moves at a constant speed of 300,000 kilometers per second, and there are many seconds in a year, we can calculate the distance of a light-year by multiplying the speed of light by the number of seconds in a year.
One light-year equals approximately 9.5 trillion kilometers, which is 9.5 x 10¹² kilometers. This measurement is practical for astronomical distances because it provides a manageable number for the vast scales involved. For perspective, even at the legal US speed limit, it would take around 12 million years to travel this distance without any stops.