About The Milky Way, to scaleDISTANCES · DATA · METHOD

The Milky Way, to scale is a free, interactive web piece: one continuous zoom from low Earth orbit, 300 km above the ground, out to the Andromeda galaxy, about 2.5 million light-years away. Every star, planet, cluster and galaxy in it sits at its measured distance and shines with its real brightness. Nothing is enlarged or brightened to stay visible, so most of space looks the way it is: dark.

It runs live in the browser on the GPU (WebGPU). No account, no install.

Open the piece

Key distances used in the piece

These are the values the piece itself uses. A parsec (pc) is 3.26 light-years (ly); an astronomical unit (AU) is the Earth–Sun distance, 149.6 million km.

Light-year and parsec conversions use 1 pc = 3.0857 × 10¹⁶ m and 1 ly = 9.4607 × 10¹⁵ m, the constants in the piece's code.

Frequently asked

How far away is the Andromeda galaxy?

The piece places Andromeda (M31) at 780 kiloparsecs, about 2.54 million light-years from the Sun. The light you see from it left 2.5 million years ago.

How big is the Milky Way?

The disc is usually quoted as about 100,000 light-years across, the figure on the piece's scale ladder. In the piece's model the spiral arms run from 2.2 to 22 kiloparsecs from the centre, and the faint stellar halo reaches about 45 kiloparsecs.

Where is the Sun in the Milky Way?

8.178 kiloparsecs (about 26,700 light-years) from the Galactic Centre, and 20.8 parsecs above the disc's mid-plane, on the Local (Orion) Spur between the Sagittarius–Carina and Perseus arms. The piece moves it round the Galaxy at 233 km/s; one orbit, a galactic year, takes about 227 million years in its model.

How many stars are in the Milky Way, and how many does the piece draw?

An estimated 100 to 400 billion. No computer can draw them one by one, so the piece splits them on the only line that matters to an eye: the stars you could individually resolve from where you are become points (2.5 million at the default quality setting, up to 10 million on the highest), and the rest are rendered as the integrated glow of their light, dimmed and reddened by dust.

What is at the centre?

Sagittarius A*, a black hole of about 4.2 million solar masses. The piece derives the mass from the orbit of the star S2, which goes round it every 16.05 years.

What do I need to run it?

A browser with WebGPU: a recent Chrome, Edge, Safari or Firefox that supports it. A laptop GPU is enough; the quality setting (⚙ in the piece, or Q) scales it.

What “to scale” means here

The governing idea is that distance is only felt if nothing lies about it.

• Light falls off with distance. A star dims as 1/d² and disappears when its flux drops below a visibility floor, by default about magnitude 11.8. That is why the real sky between the stars is black, and why it is here.
• Dust hides things. A three-dimensional dust field reddens and swallows the light behind it, so the Galactic Centre is hard to see from the Sun, as it is.
• Planets only reflect. They are lit by their star alone, so from the next star over you cannot see them.
• Sizes are true. The Oort cloud really is that much larger than the planets' orbits, and the Sun really is that far out from the centre.

On screen, a logarithmic ladder runs from low Earth orbit to Andromeda, every rung a distance, with a marker that slides as you zoom. Next to it, how long light takes to cross what you are looking at.

The galaxy model

The Milky Way is a continuous density field, not a picture:

• a thin disc (scale length 2.6 kpc, scale height 300 pc) and a thick disc (3.6 kpc, 900 pc);
• a boxy bulge and a bar about 4.6 kpc in half-length, 25° off the Sun–centre line;
• six spiral arms (Norma, Scutum–Centaurus, Sagittarius–Carina, the Local Spur, Perseus and the Outer arm), placed on the reference points and pitch angles of Reid et al. (2019), rotating at a pattern speed of 25 km/s/kpc;
• a stellar halo out to about 45 kpc, and the dust that carries the extinction.

For every pixel the renderer integrates starlight through that field against the dust's absorption, the quantity a telescope pointed at a star cloud measures. The stars that are individually above the visibility floor from the camera's position are drawn on top as points, sampled from the model's stellar populations.

Real objects in it

• The 88 constellations, with their Sky & Telescope figures and the 721 stars they are drawn between, placed in 3D at their real distances, so the figures come apart as you leave the Sun.
• Every star within 5.2 pc and the best-known bright stars, typed in by hand from published values.
• Open and globular clusters, planetary nebulae, molecular clouds, supernova remnants and nearby galaxies from published catalogues.
• 306 planetary systems within 30 pc (510 known exoplanets), from the NASA Exoplanet Archive.
• The Solar System's planets and moons, 25,000 main-belt asteroids on their JPL orbits, the Kuiper belt, the Oort cloud, Voyager 1 and 2, and the Webb telescope at L2.
• The Earth as measured now: the ISS on its current orbit, the past week's earthquakes, the cloud deck, rain and snow, tropical cyclones and the aurora sized by the geomagnetic Kp index, all from live public feeds.

Every catalogue, paper and feed is listed with credits on the sources page.

Also in the piece

• How a star dies: a star's collapse, from the main sequence to white dwarf, neutron star or black hole, on a logarithmic clock.
• Mining the Solar System: what it would really cost to go and get an asteroid.

Who made it

Galactic Space is an independent art and science project. The piece is free to use, with no ads and no tracking cookies.