When measuring vast distances in the universe, units like kilometer and mile are not practical. The distances between stars and galaxies are measured in light-years. What is a light-year? How much is a light-year in kilometers and miles? Let’s learn.
What is a light-year?
Light-year is not a unit of time. It is a unit of distance. 1 light-year is the distance light travels in one year.
Light may seem fast, but in the vastness of the universe, it is slow. In a vacuum, such as space, light travels at a speed of approximately 299,792 km/s (or about 186,282 miles per second).
To put it into perspective, imagine a beam of light traveling from the Earth to the Moon. The average distance from the Earth to the Moon is about 384,400 km (238,900 miles). It takes light approximately 1.28 seconds to cover this distance.
Now, if we extend this journey to cover the distance from the Earth to the Sun, which is about 150 million km (93 million miles), light takes about 8 minutes and 20 seconds to complete the journey.
Now, let’s take it a step further. The nearest star to our solar system, Proxima Centauri, is located about 4.24 light-years away. This means that the light we see from Proxima Centauri today actually left the star over four years ago. In other words, when we look at Proxima Centauri, we see it as it appeared four years ago, not as it is in the present.
How much is 1 light-year in kilometers and miles?
We know that distance = speed × time
1 light-year = speed of light × 1 year
= 299792.458 km/s × 1 year = 299792.458 km/s × (365.25×24×60×60) s
= 9.461 trillion kilometers (5.879 trillion miles)
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