What is the definition of a light year?

The concept of a light year is defined as the distance that light travels in one year, which is approximately 5.88 trillion miles. This measurement is fundamental in astronomy as it provides a way to express vast distances across the universe in a more comprehensible manner. Given the speed of light, which is about 186,282 miles per second, when you calculate how far light travels over the span of an entire year, it culminates in this impressive figure.

In contrast to other options, discussing the distance light travels in a week does not accurately capture the definition of a light year, which is specific to the time frame of one year. Similarly, stating the speed of light in a vacuum is relevant in the context of understanding how distances (like light years) are derived, but it does not define what a light year actually is. Additionally, mentioning the time it takes for light to reach Earth from the Sun pertains to the concept of astronomical time scales and light travel times, but it doesn’t encapsulate the broader definition of a light year as a measure of distance. Therefore, option A is the most accurate definition.