What is a light year?

Rather confusingly, a light year is actually a measurement of distance not time.

A light year shows the distance that light travels through a year, and travels at an incredible speed of 300,000 kilometres a second.  It is possible for a light year to travel around the circumference of the Earth 7.5 times per second.

light year scale - Bob King
Image Credit: Bob King & EarthSky

So one light year measures just under 10 million kilometres.  On average it takes light 8.3 minutes to travel from the Sun to the Earth.

The nearest star is 4.2 light years away and the Andromeda Galaxy is the nearest large galaxy outside our own and is about 2.5 million light years away.

The Andromeda Galaxy can actually be seen from the United Kingdom and it has looks like an elongated fuzzy blob to the naked eye.

The Hubble Telescope has detected an object in space which is believed to be around 13.2 billion light years away.  In the time it’s taken the light to reach us on Earth the original object, a compact mini galaxy would no longer exist.