The Milky Way: our home galaxy's calendar
You have been riding around the galaxy since the day you were born. Work out how far — then learn when, in the year, the Milky Way's heart is in view.
Enter a date to see how far the Sun has carried you around the galaxy.
Inside the Milky Way
We see our galaxy edge-on from inside, which is why it appears as a band of light rather than a spiral. It is a barred spiral: a bar of old stars crosses the centre, two major arms and several minor ones curl outwards, and a near-spherical halo of ancient stars and dark matter surrounds the whole thing.
- Disk diameter≈ 100,000 ly
- Stars100–400 billion
- Sun to the centre≈ 26,700 ly
- Central black hole4.3 million Suns
- Sun's orbital speed≈ 230 km/s
- One orbit (galactic year)≈ 230 million years
At the very centre sits Sagittarius A*, a black hole of about 4.3 million solar masses. The 2020 Nobel Prize in Physics went to Reinhard Genzel and Andrea Ghez for tracking stars whipping around it, and the Event Horizon Telescope published the first image of its shadow on 12 May 2022.
The Milky Way in different light
Our eyes see only a thin slice of the light the galaxy gives off. Each kind of light picks out something different, and switching between them is one of the best ways to understand what the Milky Way is made of. This view is centred on the galactic centre, with the plane of the galaxy running across the middle.
The whole Milky Way, in five kinds of light
Real survey images you can zoom and drag, from the Strasbourg astronomical data centre (CDS).
Visible light, as your eyes would see it from a perfectly dark site. Dark lanes are dust clouds blocking the stars behind them.
Viewer: Aladin Lite, CDS Strasbourg. Images: Axel Mellinger all-sky mosaic; 2MASS (UMass/IPAC); Planck (ESA); HI4PI survey; Fermi LAT (NASA).
A calendar of the Milky Way
- ≈ 13 billion years ago
The oldest stars of the halo and thick disk form; parts of the galaxy are almost as old as the universe.
- ≈ 8–11 billion years ago
The Milky Way absorbs a dwarf galaxy now called Gaia-Enceladus (or Gaia-Sausage-Enceladus), whose stars still move on telltale elongated orbits.
- ≈ 8–9 billion years ago
The thin disk — where the Sun lives and where most stars form today — settles into shape.
- 4.6 billion years ago
The Sun forms from a collapsing gas cloud, probably in a cluster of sibling stars that has since dispersed.
- Ongoing
The Sagittarius dwarf galaxy is being torn apart as it plunges through the disk; its passages may have triggered bursts of star formation.
- In about 4–5 billion years
Possible close encounter or merger with Andromeda — see the Andromeda page for the latest odds.
Milky Way season: when to see the core
The brightest part of the Milky Way — the star clouds towards the galactic centre in Sagittarius and Scorpius — is a seasonal sight. It is behind the Sun in December and January and climbs into the evening sky through the middle of the year.
| Latitude | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 40° N (Delhi to New York) | — | — | — | — | — | 8° | 19° | 20° | 10° | — | — | — |
| 20° N (Mumbai, Mexico City) | — | — | — | — | 0° | 23° | 38° | 39° | 26° | 4° | — | — |
| 30° S (Durban, Perth) | — | — | — | 1° | 24° | 49° | 75° | 79° | 52° | 28° | 4° | — |
Height of the galactic centre above the horizon at 9 p.m. local time on the 15th of each month. Green is well placed; dashes mean it is below the horizon then. Pick a moonless night away from city lights — the core is invisible from most cities.
In the northern hemisphere the core season runs roughly from March (pre-dawn) to October (early evening), best in June–August, low in the south. South of the equator it rides high overhead in the June–August winter nights — the southern sky is where the Milky Way is at its most spectacular.
What the world calls it
The word galaxy itself comes from the Greek galaxías kýklos, "milky circle", so every galaxy is named after ours. Elsewhere it's a river: Akashganga, the Ganga of the sky, in Hindi and Sanskrit; the Silver River (Yínhé) in Chinese, across which the cowherd and the weaver girl meet once a year at the Qixi festival; the River of Heaven (Amanogawa) in Japanese, celebrated at Tanabata on 7 July. In Swedish it's the Winter Street; in Arabic and Persian, the straw path.
A map of our galaxy
Astronomers piece the map together from radio and infrared surveys, star distances measured by ESA's Gaia satellite, and the motions of gas clouds. Two large arms — Perseus and Scutum–Centaurus — start from the ends of the central bar; smaller arms and spurs fill the gaps. The Sun sits on the Orion Spur, a short bridge between two major arms.
Spiral arms aren't fixed structures that stars belong to. They behave more like traffic jams: stars and gas slow down and crowd together as they pass through, which triggers star formation and makes the arms glow with young blue stars. The Sun has crossed several arms in its lifetime.
Tonight's Milky Way
The bright band is the disc of our galaxy seen edge-on. Where it runs through Cygnus to Sagittarius you can see the Great Rift, a long dark split caused by dust clouds a few thousand light-years away. The chart shows where the band and the galactic centre are above your city right now — and you can slide forward to see later tonight.
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Times are shown in your device's own time zone.
How to read it: the centre is straight overhead and the rim is the horizon. Hold it above your head with N towards north — east and west are swapped compared with a map because you're looking up, not down.
Galactic coordinates
For mapping the galaxy, astronomers use a coordinate grid aligned with it rather than with Earth. Defined by the International Astronomical Union in 1958, galactic longitude (l) runs along the plane of the Milky Way starting at 0° towards the centre in Sagittarius, and galactic latitude (b) measures how far above or below the plane something is. The north galactic pole lies in Coma Berenices. The Sun's orbit carries us towards l = 90°, in the direction of Cygnus.
Frequently asked questions
How old is the Milky Way?
Its oldest stars are about 13 billion years old, so parts of the galaxy formed less than a billion years after the Big Bang. The thin disk where the Sun lives formed later, roughly 8–9 billion years ago.
How far is the Sun from the centre of the Milky Way?
About 26,700 light-years (8.18 kiloparsecs), roughly halfway out from the centre to the edge of the disk.
When is the best time to see the Milky Way?
For the bright core, June to August evenings in the northern hemisphere and May to September in the southern hemisphere, on a moonless night from a dark site.
How many stars are in the Milky Way?
Somewhere between 100 and 400 billion. Most are small red dwarfs too faint to see without a telescope.