On a very dark, clear night — far from city lights — you can see a faint, misty band stretching across the sky. Ancient people called it many things; the Greeks called it the Galaxias Kyklos, the Milky Circle. Today we know it as the Milky Way, and it's not a cloud or a smear of dust. It's the galaxy we live in, seen edge-on from the inside.
What a galaxy actually is
A galaxy is an enormous collection of stars, gas, dust, and dark matter, all held together by gravity and slowly rotating around a central point. The Milky Way contains somewhere between 100 and 400 billion stars. Our sun is just one of them — a perfectly ordinary, middle-aged yellow star sitting in one of the galaxy's outer spiral arms.
Imagine standing inside a vast forest. You can't see the whole forest — all you can see are trees in every direction. When you look towards the denser part of the forest, you see more trees crowded together. That's why the Milky Way appears as a bright band: we're looking towards the dense centre of our galaxy, with billions of stars packed tightly behind each other. When we look away from the band, we're looking outward toward the galaxy's edges — fewer stars, more empty space.
The shape we can't see
We know the Milky Way is a barred spiral galaxy — a large disc with elegant spiral arms curving outward from a central bar-shaped cluster of stars. We know this from studying other galaxies and from mapping the positions of stars around us using telescopes. But we'll never photograph our own galaxy from the outside, because we're deep inside it and no spacecraft will be able to escape it in any human timescale.
How big is it?
The Milky Way is about 100,000 light-years across. Light travels at 300,000 kilometres per second — the fastest anything can move — and it would still take 100,000 years to cross from one side to the other. Our sun is about 26,000 light-years from the galactic centre. It takes the sun (and us with it) about 225 million years to complete one orbit of the galaxy. That's called a cosmic year.
What's in the middle?
At the very centre of the Milky Way sits a supermassive black hole called Sagittarius A*, with a mass about 4 million times that of our sun. In 2022, the Event Horizon Telescope captured the first actual image of it. Don't worry — it's 26,000 light-years away and poses no danger to us whatsoever.
On a very dark, clear night, far from city lights, you can see something amazing. There is a faint, misty band stretching across the sky. Long ago, the ancient Greeks called it the Galaxias Kyklos, which means the Milky Circle. Today we call it the Milky Way. It is not a cloud or a smear of dust. It is the galaxy we live in, seen from the inside.
What a galaxy actually is
A galaxy is a huge group of stars, gas, dust, and dark matter. Gravity holds it all together, and it slowly spins around a central point. The Milky Way has between 100 and 400 billion stars in it. Our sun is just one of those stars. It is a normal, middle-aged yellow star. It sits in one of the outer arms of our galaxy.
Imagine standing in the middle of a huge forest. You cannot see the whole forest from inside it. All you can see are trees in every direction. When you look towards the busiest part of the forest, you see lots of trees packed closely together. The Milky Way looks like a bright band for the same reason. We are looking towards the busy centre of our galaxy. Billions of stars are packed tightly behind each other there. When we look away from the band, we are looking towards the edges of the galaxy. There are fewer stars and much more empty space out there.
The shape we cannot see
The Milky Way is a barred spiral galaxy. Think of it like a giant Catherine wheel firework. It has a flat disc shape with curving arms that spiral out from a bar of stars in the middle. We know this from studying other galaxies. We have also mapped the positions of stars around us using telescopes. We will never be able to take a photo of our galaxy from the outside. That is because we are deep inside it. No spacecraft could ever travel far enough out in a human lifetime.
How big is it?
The Milky Way is about 100,000 light-years across. Light travels at 300,000 kilometres per second. That is the fastest that anything can move. Even at that speed, it would take 100,000 years to cross the galaxy. Our sun is about 26,000 light-years away from the centre of the galaxy. It takes the sun about 225 million years to travel all the way around the galaxy once. Scientists call this amount of time a cosmic year.
What is in the middle?
At the very centre of the Milky Way there is a supermassive black hole. It is called Sagittarius A*. It has a mass about 4 million times bigger than our sun. In 2022, a group of telescopes called the Event Horizon Telescope took the first real image of it. Do not worry though. It is 26,000 light-years away from us. It is no danger to us at all.