The Milky Way
This year, scientists have discovered a planet we could live on; a new black hole, and the edge of the Milky Way. Our galaxy holds secrets we continue to unlock. But what do we already know?
How did the Milky Way get its name?
One of the most striking features visible in a truly dark sky, when Moonlight isn’t so bright, is the band of pale white stretching across the sky. It is our view of the huge system of stars we call the Milky Way.
Before we knew what it was, different cultures told their own folktales to explain it. One African tribe believed it was smoke from their ancestors’ campfires; Native American stories tell of processions of animals in the sky. It was the ancient Greeks who gave our galaxy its name, comparing it to a stream of spilt milk.
Who discovered it?
Generations of people had wondered at the Milky Way, without fully understanding it, until 1610 when Italian astronomer Galileo Galilei studied the mysterious beauty through a telescope. He discovered it was composed of many individual stars. We now know that the system we live in contains billions of stars and planets. We also know that the Milky Way is just one galaxy among many billions of others in the Universe.
What does it look like?
In 1785, William Herschel made the first important discovery about the structure of the Milky Way: it was shaped like a disc. The Milky Way is a spiral galaxy. Its core is surrounded by a flat disk of gas about 120,000 light-years wide. Spiral arms made up of billions of stars swirl out from the centre. Our Sun is one of these stars, located about 27,000 light-years from the galactic core.
Do we see the stars in real time?
No. In fact, many of the stars we see have already died. This is because the galaxy is so enormous that it takes thousands of years for light to travel through it. Light from stars really comes from a long time ago. Even the light from the Sun is about 15 minutes behind. So, when we observe our galaxy, we are really looking into the past.
How does it keep its spinning shape?
Galaxies are held together by gravity. Scientists believe it down to supermassive black holes, which have such a strong gravitational pull that not even light can escape. There is probably one at the centre of the Milky Way, holding the stars in their swirling vortex.
How much of the galaxy have we explored?
On 25 August 2012, space probe Voyager 1 entered interstellar space. It had taken 35 years to reach the edge of our solar system and travel 13 billion miles (just 0.2 light-years). More recently, powerful telescopes have discovered planets as far as 5,000 light-years away. But scientists now believe the galaxy is 2-million-light-years wide, meaning much of it remains a mystery.
Gaia satellite is currently on a mission to make a 3D map of the Milky Way. When Gaia finishes in 2022, it will have studied more than one billion stars and revealed far more about our extraordinary galaxy.
- Would you like to travel to another galaxy?
- Invent a new galaxy and give it a name. Draw a map of it, and design some of the planets that exist inside it.
- A system of millions or billions of stars, gas and dust, held together by gravitational attraction.
- One light-year is the distance that light can travel in 365 days – about 6 trillion miles.
- Relating to a galaxy. Inter-galactic travel is travelling between different galaxies.
- Travelling at 186,000 miles per second, light is the fastest thing in the Universe, as far as we know.
- Supermassive black holes
- The largest type of black hole. Believed to be created when stars die, black holes have such strong gravity that they consume everything surrounding them.
- A mass of wind or liquid that spins round so fast, it pulls objects into its centre.
- Interstellar space
- Literally means “between stars”; open space that is not part of a solar system.