fényév

A fényév is a unit of astronomical distance. It represents the distance that light travels in a vacuum in one Julian year. The speed of light in a vacuum is approximately 299,792,458 meters per second. Over the course of a Julian year, which is precisely 365.25 days, light covers an enormous distance.

One light-year is equivalent to about 9.461 trillion kilometers or about 5.879 trillion miles. This unit is primarily used to measure distances to stars, galaxies, and other celestial objects outside our solar system. Because the universe is vast, using kilometers or miles to describe these distances would result in extremely large and unwieldy numbers. The light-year provides a more manageable scale for astronomical measurements.

For example, the nearest star to our Sun, Proxima Centauri, is about 4.24 light-years away. This means that the light we see from Proxima Centauri today left the star over 4 years ago. The Andromeda Galaxy, our closest large galactic neighbor, is approximately 2.537 million light-years away. Understanding the concept of a light-year is crucial for comprehending the immense scales of the cosmos and the time it takes for light from distant objects to reach Earth.