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How big is the Universe?

Measuring in space

Normal measurements like miles don't work in space. Everything is too big. So scientists use something called light-years to measure distances in space.

A light-year is the distance light travels in one year. Light travels at a speed of 186,282 miles per second, so in a year it travels 5.8 trillion miles. That means one light year measures 5.8 trillion miles.


To understand the size of the Universe and how big a light year is, we need to start with our home. Earth.

Earth is the only planet in the known Universe that we know for certain supports life. It measures 24,900 miles around the equator.

To give you an idea of how fast light travels, at the speed of light you could travel around the Earth’s equator 7 times in a single second.

Our solar system

A solar system is a group of planets and stars bound together by the force of gravity. Earth shares a solar system with 7 other planets and a star we call the sun.

Our solar system is big, but compared to the Universe, it’s still tiny.

The size of our solar system is is not even one whole light year. If you were travelling at the speed of light, it would take 8 minutes to travel from the Sun to Earth.

The distances from our sun to the planets around it

Image showing distance of planets from the sun measured by speed of light

The milky way

A galaxy is a group of solar systems, stars and planets bound together by gravity. Galaxies contain billions of stars.

Our solar system lives in a galaxy called Milky Way and our Sun is just one of around 400 billion stars that live in it.

The Milky Way is around 150,000 to 200,000 light years across. So if our solar system was the size of a £1 coin, the Milky Way would be the size of the United States.

Local group

The Milky Way is part of a bigger group of galaxies which scientists have named the Local Group. It measures 10 million light years across.

Compared with our solar system, which we can measure in light minutes, it would take millions of years for light to travel from one side of the Local Group to the other, and it doesn’t stop there.

Even at its colossal size, the Local Group is a part of an even bigger cluster of galaxies called the Laniakea Supercluster.

Laniakea Supercluster

The Laniakea Supercluster measures 520 million light years across and contains around 100,000 galaxy, including ours, the Milky Way.

It is one of 5 superclusters containing millions of galaxies which takes us to the limit of what we as humans have discovered so far.

Scientists estimate that all the planets, stars and galaxies that we know about make up only 4 percent of the whole Universe.