The light year wasn't "discovered" in the sense of a new phenomenon being found. It's simply a unit of measurement, like a meter or a mile.

Here's a breakdown:

* The concept of light traveling at a finite speed: This was first established in the 17th century by scientists like Ole Rømer and Christiaan Huygens.

* The first use of "light year" as a unit of distance: While the idea of using the distance light travels in a year was likely discussed earlier, the term "light year" is believed to have been first used in 1838 by German astronomer Friedrich Bessel.

So, while we can pinpoint when the term was first used, the concept of using light's speed to measure distance is an evolution of understanding light's properties, a process that took centuries.