The Milky Way
Galaxy · Barred spiral · Our home
The Milky Way is our home galaxy – a huge spinning disc of stars, gas and dust with a bar in the middle and spiral arms. The Sun is in one of the arms. The pale band of light across a dark sky is the galaxy seen edge-on from inside.
- 26,700 light-years awayEven light – the fastest thing there is – needs 26,700 years to get here.
- ~100,000 light-yearsWidth
- 100–400 billionStars
Take a closer look
Ingredients of a Galaxy
Besides stars, the Milky Way holds vast clouds of gas and dust – the raw ingredients for new suns and planets. At its very centre sits a black hole called Sagittarius A*, about 4 million times heavier than the Sun. Wrapped around everything is an invisible halo of dark matter.
Riding the Galactic Carousel
Even when you sit perfectly still, the Sun is carrying you around the galaxy at roughly 230 kilometres every second – fast enough to get from London to New York in about 25 seconds. Our spot, about halfway out from the centre, is a quiet suburb far from the crowded core.
Seeing Through the Dust
Thick dust hides the galaxy’s centre from ordinary telescopes, like fog hiding a lighthouse, but infrared and radio telescopes see straight through it. By tracking stars whizzing around the centre for decades, astronomers proved a giant black hole lives there – work that won the 2020 Nobel Prize in Physics.
How we found out
- Ancient times
The Greeks saw a river of milk (“galaxias”, which gives us the word galaxy). In India it is Akash Ganga – the river of the sky.
- 1610
Galileo shows the band is made of countless faint stars.
- 1785
William Herschel counts stars to map the galaxy’s shape.
- 1918
Harlow Shapley shows that the Sun is not at the centre of the galaxy.
- 2013–2025
The Gaia spacecraft maps the positions and motions of nearly 2 billion stars.
How can we know the shape of the galaxy if we are inside it?
Like mapping a forest from inside it: astronomers measure distances and motions of millions of stars and gas clouds, then put the 3D picture together.
See it yourself
Get far away from city lights on a moonless night and look for a faint, cloudy band stretching across the sky.
From the encyclopedia
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