AI reviewed · sources pending. Book associations have not been verified.
Light-year
VocabularyA light-year is the distance light travels in a vacuum in one year.
Explanation or usage
A light-year is a unit of distance: the distance light travels in a vacuum in one year. Because light takes time to reach us, we observe distant objects as they were when their light departed. For very distant objects, cosmological expansion makes the relationship between distance and light-travel time more complex.
Common misunderstandings
A light-year is simply a unit of elapsed time.
In Cosmos
General context reviewed · book attribution and sources pending
Astronomical distance can be discussed by distinguishing distance from elapsed time.