What is a light year?

A light year is a unit of distance used in astronomy to measure vast distances in space, but contrary to what its name suggests, it has nothing to do with time, but with the distance light travels in a year.

One of the first scientists to put forward the idea that light has a finite speed was the Danish astronomer Ole Romer in the 17th century.

Romer was the first to calculate a rough estimate of the speed of light by observing the variations in the time at which the moons of Jupiter appeared and disappeared behind Jupiter.

From his calculations, he estimated the speed of light to be about 220,000 kilometres per second, which was quite close to the true value.

The speed of light in a vacuum is about 299,792 kilometres per second. So, if we multiply that speed by the number of seconds in a year, which is about 31,536,000, we get the distance light travels in a year, which is about 9.46 trillion kilometres.

So when we say that something is one light year away, we mean the distance that light would have to travel in one year to reach that object. This is one way of understanding the vast distances in the universe.

However, it is important to note that a light year is an astronomical measurement and not a unit of time. It doesn't mean that it would take us a year to get there in a spaceship, as we don't currently have the technology to travel at near-light speeds.