lightseconds

Light-second is a unit of distance used in astronomy. It is defined as the distance that light travels in vacuum in one second. In numeric terms, 1 light-second (abbreviated ls) equals c × 1 s, about 299,792.458 kilometers. The term is commonly written as light-second or simply ls.

The light-second is convenient for expressing distances where the relevant quantity is light travel time. It is related to other time-based distance units such as the light-minute and the light-hour, and to the astronomical unit (AU). For context, 1 AU is about 499.0 light-seconds.

Conversions and example distances: 1 ls ≈ 299,792.458 km. 1 light-minute ≈ 17,987,547 km. 1 light-hour ≈ 1,079,252,849 km. The Moon is about 1.28 light-seconds away on average, the Sun is about 499 light-seconds away, and Proxima Centauri is about 134 million light-seconds away, roughly 4.2 light-years.

Usage and scope: Light-seconds are commonly employed when discussing distances within the Solar System or the light-travel time relevant to spacecraft communications. For longer cosmic scales, other units such as light-years or parsecs are typically used, with light-seconds serving as a bridge between distance and travel time in discussions of astronomical optics and navigation.