What is the Milky Way? Our home galaxy, explained simply

Seen from outside, the Milky Way would look like a giant pinwheel. Its main parts are:

• The central bulge and bar: a dense, elongated crowd of mostly older stars around the centre.
• The disc: the broad, thin, flat region that holds most of the galaxy's visible stars, gas and dust.
• The spiral arms: curving regions within the disc where gas is densest and new stars are born. The Sun lies in a smaller arm called the Orion Arm, or Orion Spur.
• The halo: a much larger, roughly round region around the disc, with old stars, tight balls of stars called globular clusters, and most of the galaxy's dark matter.

No one has ever photographed the Milky Way from outside, because no spacecraft has gone anywhere near far enough. Every picture showing the whole spiral is either an artist's impression built from measurements, or a photo of a similar galaxy.

Because we live inside the disc. When you look along the plane of the disc on a dark night, you are looking through thousands of light-years of stars, too faint and too many to see one by one, so their light blends into a soft glowing band. Dark lanes and patches within it are clouds of dust blocking the light of stars behind them.

The ancient Greeks called it the milky circle, and the word galaxy itself comes from the Greek word for milk. In India the band has long been called Akashganga, the Ganga of the sky. Its brightest part, towards the galaxy's centre in the constellation Sagittarius, is highest in the evening sky from about June to September.

You need a clear, moonless night far from city lights; a date close to Amavasya, the new moon, is best (see moon phases). Ladakh has some of India's darkest skies: in 2022 the area around the Indian Astronomical Observatory at Hanle became India's first dark sky reserve. Remote parts of Spiti, the Rann of Kutch and the Rajasthan desert can also show the Milky Way clearly.

A free sky app such as Stellarium will show you exactly where the band will be from your location before you set out.

A supermassive black hole called Sagittarius A*, about 4 million times the mass of the Sun. Astronomers worked out its mass by tracking stars racing around it, work that won the 2020 Nobel Prize in Physics, and the Event Horizon Telescope released the first image of it in May 2022. It is about 26,000 light-years away and poses no danger to Earth.

Possibly, but it is less certain than the textbooks say. For more than a decade the standard prediction was a collision with the Andromeda Galaxy in about 5 billion years. A study published in June 2025, using data from the Hubble and Gaia space telescopes, found roughly a 50-50 chance of the two galaxies merging within the next 10 billion years, and only about a 2 percent chance of a collision in the next 4 to 5 billion years.

Even if it happens, stars are so far apart that they would almost never hit each other. It is a slow rearrangement over billions of years, not a crash.

No one knows exactly, but surveys of exoplanets suggest that, on average, there is at least one planet for every star in our galaxy. That would mean hundreds of billions of planets and a vast number of planetary systems. More than 6,000 planets around other stars have been confirmed so far, most of them within a few thousand light-years of Earth.

Our galaxy is the subject of lesson 9 of Astronomy 101, the WhyCosmos live course for ages 8 to 16, and lesson 10 places it on the scale ladder from the Sun to the Local Group of galaxies.