Define 'light year.'

A light year is defined as the distance that light travels in a vacuum in one year. This unit of measurement is used in astronomy to express distances on a cosmic scale, where the vastness of space makes traditional units like kilometers or miles impractical. Given that light travels at an approximate speed of 299,792 kilometers per second (or about 186,282 miles per second), this results in a significant distance when scaled up to a year.

For example, in one year, light travels about 9.46 trillion kilometers (or about 5.88 trillion miles), which illustrates just how vast the distances between celestial objects can be. Using light years allows astronomers to easily convey these large distances and makes it easier for scientists and the public to understand the scale of the universe.

This clarification highlights why the other choices are less suitable. The option suggesting the time taken by light to travel one year conflates distance with time, while the option identifying a light year as a measure of time in astronomy fails to capture the essence of its definition, which is fundamentally about distance. Lastly, referring to the speed of light does not encompass the conceptual meaning of a light year, as it is more about the distance rather than the speed at which light