A light year is a unit of measurement of

A light-year is a fundamental unit of measurement used in astronomy to describe very large distances [2]. Despite containing the word 'year', it is explicitly a measure of distance and not of time [1]. It is defined as the total distance that light travels in a vacuum during one Julian year (365.25 days). Given that light travels at a velocity of approximately 300,000 km/second, one light-year equals roughly 9.46 trillion kilometers [1]. This unit is essential for measuring vast scales, such as the diameter of the Milky Way galaxy, which is between 150,000 and 200,000 light-years [2]. While other units like the parsec exist for professional astronomical calculations, the light-year remains the standard for expressing the immense gaps between stars and galaxies.

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