What is the common unit of measurement for astronomical distances?

The common unit of measurement for astronomical distances is the light year. A light year is defined as the distance that light travels in one year in a vacuum, which is about 5.88 trillion miles or approximately 9.46 trillion kilometers. Using light years simplifies the discussion of astronomical distances because the vastness of space means that conventional units like kilometers or miles would result in exceedingly large and cumbersome numbers, making it difficult to conceptualize distances to stars or galaxies.

While parsecs and light years are both used in astronomy, the light year is often more popular and intuitive for general discussions since it directly relates to the speed of light—a fundamental constant in physics that underscores the nature of light and its travel across the universe. Parsecs, although useful for professional astronomers, specifically quantifies distances in a way that is slightly less intuitive for the general public compared to the light year.