Astronomy Units – Meaning of a Light-Year In astrophysics and space science, the unit “light-year” is used to measure:

Introduction / Context:
Cosmic distances are vast, making kilometers impractically large for routine discussion. Astronomers therefore use specialized units like the light-year, parsec, and astronomical unit to express separations between celestial objects efficiently.

Given Data / Assumptions:

• The light-year relates to the distance light travels in vacuum in one Julian year.
• It is not a measure of velocity despite the word “year.”
• Used commonly for stars and galaxies beyond the Solar System.

Concept / Approach:
A light-year is a unit of distance. Light travels approximately 9.46 * 10^12 km in one year, so distances to nearby stars (e.g., Proxima Centauri ~4.24 ly) are conveniently expressed in light-years. Speeds, by contrast, are given in km/s or m/s, not light-years per time.

Step-by-Step Solution:

Verification / Alternative check:
Introductory astronomy texts consistently define the light-year as a distance unit, alongside the parsec (~3.26 ly) and the astronomical unit (~1.496 * 10^8 km).

Why Other Options Are Wrong:

• Speed of satellites/ships/rockets: These require distance per time (e.g., km/s), not a distance-only unit.

Common Pitfalls:
Misinterpreting the word “year” as time in the unit name. It simply anchors the distance to how far light travels over that time span.

Final Answer:
distance between bodies in the universe