Light year is a unit for measurement of

A light year is a fundamental unit of measurement used in astronomy to express very large distances. Despite the word 'year' in its name, it is a measure of distance rather than time [2]. It is defined as the distance that light travels in a vacuum in one Julian year [1]. Given that light travels at a speed of approximately 300,000 km/second, one light year equals roughly 9.46 trillion kilometers [1]. This unit is essential for measuring the vast scales of the universe, such as the distance between stars and galaxies, where standard units like kilometers or miles are impractical [2]. For instance, the Milky Way galaxy's diameter is estimated to be between 150,000 and 200,000 light years [2], and the nearest star system, Proxima Centauri, is about 4.2 light years away.

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 2: The Origin and Evolution of the Earth > The Star Formation > p. 14
2. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 1: The Universe, The Big Bang Theory, Galaxies & Stellar Evolution > Our Galaxy (The Milky Way) > p. 8