Final answer:
Light from stars takes thousands of years to reach us due to the immense distances involved, with the term 'light-year' denoting the distance light travels in one year. The time it takes for light to reach Earth from a star is a direct measurement of its distance, not its brightness, color, or size. Measuring star distances is complex due to varying star luminosities.
Step-by-step explanation:
The light we see from stars takes thousands of years to reach us primarily because of their distance from the Earth. The stars we observe at night are incredibly far away, and light, even though it is the fastest-moving thing in the universe, traveling at about 300,000 km/s, takes a significant amount of time to cover these vast stretches of space. The concept of a light-year, which is the distance light travels in one year, helps us comprehend the immense distances involved. Moreover, the brightness or apparent brightness of a star does not solely determine how far away it is due to the variety of intrinsic luminosities stars possess. Measuring the actual luminosity and distance of stars is one of the greatest challenges in astronomy because it's not always clear if a star appears dim due to low luminosity or if it's actually positioned far away from us.