How long is a light-year per second?

The Immense Span of a Light-Year

Light, an electromagnetic wave, travels through the vacuum of space at an astonishing speed: approximately 186,000 miles (299,792 kilometers) per second. This extraordinary velocity serves as the foundation for one of astronomy’s most fundamental units of distance: the light-year.

Defining a Light-Year

A light-year is defined as the distance that light travels in one Earth year. Considering that light traverses 186,000 miles per second, it covers an immense distance over the course of a year.

Calculating the Distance

To calculate the distance encompassed by a light-year, we multiply the speed of light by the number of seconds in a year:

Distance = Speed × Time
Distance = 186,000 miles/second × 365 days/year × 24 hours/day × 60 minutes/hour × 60 seconds/minute
Distance ≈ 5.879 trillion miles

Cosmic Distances

The light-year is used to express astronomical distances that are far too vast for standard units of measure such as miles or kilometers. For example, the distance to the nearest large galaxy, Andromeda, is about 2.5 million light-years away. This means that the light we see from Andromeda today left that galaxy 2.5 million years ago.

Significance in Astrophysics

The light-year plays a crucial role in astrophysics, allowing astronomers to gauge the vastness of the universe and measure the distances to distant astronomical objects. By understanding the speed of light and the concept of a light-year, we gain insights into the immense scale and time frames of the cosmos.