# What is a Light Year?

To explain the distance between London and New York, miles is the right measurement to use. It is 3,459 miles. When you need to explain the distance the distance between Earth and the Sun, you could use miles, it is 149.6 million miles. Alternatively, you could start using new units such as Astronomical Unit.

1 A.U. is used to describe the distance bwetween the Earth and the Sun. Its most useful to use when talking about distances in the Solar System. For example, we can say Pluto is 39.5 A.U. Pluto average distance from the Sun is 39.5 x the distance between Earth and the Sun. Pluto's orbit round the Sun is elliptical and so its distance can be smaller and larger than that.

When talking about distances to stars, using A.U. can create really large numbers so we use another term, Light Years. Despite its name, a Light Year is not an unit of time but a unit of distance. A light year is the distance light can travel in a year, roughly 6 trillion (6,000,000,000,000) miles. The term was devised to make it easier to explain vast distances between objects such as stars and galaxies.

It is a lot easier to describe distance using this term, try explaining the distance between the Earth and say Proxima Centauri, the closest planet to us after the Sun. The distance between Earth and Proxima Centauri in terms of Light years is 4.22 light years, its a lot easier than saying 24,000,000,000,000 miles or thereabouts.

The distance to the Andromeda Galaxy is about 2.537 Million Light Years, can you imagine trying to express that in terms of miles.

There are other units referred to as Light Months, Light Days, Light Hours, Light Minutes and Light Seconds. I think you can work out what distances those units describe. It takes light eight light minutes to get from the Sun to the Earth.

A spaceship travelling at the speed of light, 4.23 years to travel from Earth to Proxima Centauri and another 4.23 light years to return. In Star Trek, travelling at Warp Factor is travelling many times the speed of light. It is something that according to Einstein is not possible.

According to Einstein, nothing can travel faster than light, it is maximum speed possible. For many years, people believed the Earth was at the centre of the Solar System and then it was proved otherwise. In the future, Warp Factor may well be proved possible but it isn't now.

As for Buzz Lightyear, thats a character in the Toy Story film franchise and not a unit. Buzz's catchphrase is 'To Infinity and Beyond.'