Galaxies · Space Codex
The Milky Way
A barred spiral about 100,000 light-years across holding 100–400 billion stars.
Our barred spiral home galaxy
At a glance
Key points
The Sun sits in a minor arm about 26,000 light-years from the central black hole and takes about 230 million years to circle it once.
- The Sun circles the centre every ~230 million years
- Gaia's 2025 map shows more than two spiral arms
- Gaia DR4 is due on 2 December 2026
Structure
A long bar of old stars crosses the centre. Spitzer's infrared census found two major arms rich in old stars, Scutum–Centaurus and Perseus, plus gas-rich minor arms. Gaia's 2025 map, built from about two billion stars, suggests more than two arms, less prominent than once drawn, and a bar more tilted toward the Sun.
Seen from inside
From Earth we look along the disc, so the galaxy appears as a band of light across the sky, brightest toward Sagittarius where the bulge lies and split by dark lanes of dust such as the Great Rift.
The centre
Sagittarius A* holds about 4.3 million solar masses yet looks, from Earth, about the size of a doughnut on the Moon. The Event Horizon Telescope imaged its shadow in 2022 and its magnetic field in 2024.
What we still don't know
How massive the dark halo is, how many arms there really are, and what blew the Fermi bubbles: a burst from the black hole or a wave of star formation.
Missions
- 2013–2025
Gaia
ESACompletedMapped about two billion stars; Data Release 4 is scheduled for 2 Dec 2026.
- 2017–
Event Horizon Telescope
International collaborationActiveEarth-sized radio interferometer at 1.3 mm; imaged M87* (2019) and Sgr A* (2022).
First-hand · our 3D model
How we render it
Every view in the 3D model sits inside the Milky Way. The sky is an inside-out panorama sphere in galactic coordinates, using ESO's eso0932a panorama by S. Brunier (CC BY 4.0) at 4K on desktop Explore. It is rotated into place with the IAU obliquity and the Hipparcos equatorial-to-galactic matrix, so the band of the galaxy lies where it really does relative to the planets.
In front of it are all 9,110 stars of the Yale Bright Star Catalogue at their J2000 positions. Each star's colour comes from its B−V index, converted to a temperature and then to a blackbody colour by integrating Planck's law against the CIE 1931 colour-matching functions, white-balanced so the Sun would be white. Named stars such as Betelgeuse, Rigel and Sirius land on their photographed counterparts to about half a degree.
Related entries
- Sagittarius A*The black hole at the centre of the Milky Way
- Large Magellanic CloudThe Milky Way's biggest satellite
- Andromeda GalaxyM31 · the nearest large spiral
- The Milky Way, explainedOur barred spiral home galaxy
Sources
- ESA: Gaia: the best Milky Way map (opens in a new tab)
- NASA Science: The Milky Way galaxy (opens in a new tab)
- NASA Imagine the Universe: Ask an Astrophysicist (opens in a new tab)
- GRAVITY Collaboration 2019, A&A 625 L10 (arXiv) (opens in a new tab)
- NASA Science: Solar System facts (opens in a new tab)
- Review: Milky Way mass (arXiv 2305.18408) (opens in a new tab)
- ESO: eso2208: first image of Sgr A* (opens in a new tab)
- NASA: Fermi finds giant structure (2010) (opens in a new tab)
- ESA: Gaia news 2026 (opens in a new tab)
- Cautun et al. 2019 (arXiv) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.