Consider the following statements about Light year: 1. Light year is a unit for measurement of very large distances. 2. Light year is a unit for measurement of very large time intervals. 3. Light year is a unit for measurement of intensity of light. Which of the statements given above is/are correct?

A light year is strictly a unit of distance, not time or light intensity. It is defined as the distance that light travels in a vacuum in one Earth year [2]. Because light travels at a speed of approximately 300,000 km/second, one light year equals about 9.46 trillion kilometers [1]. Statement 1 is correct as it is used to measure vast astronomical distances between stars and galaxies that are too large for kilometers or miles. Statement 2 is incorrect because, despite the word 'year', it is a measure of distance and not of time [2]. Statement 3 is incorrect as light intensity is measured in units like candela or lumens, whereas a light year measures length. Therefore, only statement 1 is correct.

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