WARPLAB

What am I looking at?

What you are looking at

A 3D map of 623 379 real galaxies round the Milky Way, measured by the Sloan Digital Sky Survey out to 844 Mpc. Fly through it to find filaments, walls and voids, the Virgo and Coma clusters and the Sloan Great Wall; turn on Laniakea's flow lines to see where gravity pulls us. Below the map, three steps show how a measured redshift becomes a distance.

Controls

On this device:

Mouse

  • Drag the map to look round; scroll to fly forward or back.
  • Point at a galaxy to read its distance, how long its light took, its redshift and its colour.
  • Click a place under Fly to (Milky Way, Virgo, Coma, Sloan Great Wall, Boötes void, Great Attractor) to fly there. Back to the start returns.
  • Click Survey footprint, 100 Mpc rings, Laniakea flows or Density to show or hide each layer; Colour by switches between distance and the galaxies' own colour.
  • In the guide, click a step and drag Redshift; the charts and numbers follow.
  • Click the badge beside a number for its source and licence.

Keyboard

  • Tab to the map, then W, A, S and D fly, Q and E sink and rise, and the arrow keys turn. Hold Shift to go four times faster.
  • Tab to a place or a layer button and press Enter or Space.
  • On the guide's steps, the left and right arrows switch step; on the Redshift slider, the arrows move it.
  • H or ? opens this panel. Esc closes it.
Other devices

Touch

  • Drag the map with one finger to look round; pinch with two to fly forward or back.
  • Tap a galaxy for its numbers.
  • Tap a place to fly there, and a layer button to show or hide it.
  • In the guide, tap a step and slide Redshift.

Headset and AR

  • On a headset, Enter VR floats you inside the map at the Milky Way, where 1 m is 10 Mpc: Virgo is 1.6 m away, Coma 10 m, the survey's edge 84 m.
  • Push the left stick to fly the way you look; the right stick turns 30° at a time.
  • Point a controller or your hand at the panel and pull the trigger or pinch to press. Press a place to jump next to it; press a layer to show or hide it.
  • The panel reads out how far you are from home, how long light from home takes to reach you and the redshift there.
  • The first session opens a short intro that teaches these controls; Controls on the panel opens it again. Exit VR is on the panel.

Glossary

Redshift z
How much a galaxy's light has been stretched on its way: every wavelength arrives 1 + z times longer. SDSS measures it from the lines in each galaxy's spectrum.
Why it matters It is the one number SDSS measures for every galaxy; the map turns it into a distance.
Hubble's law
Nearby, a galaxy's redshift times the speed of light (cz) is proportional to its distance: d = cz / H0. Here H0 = 67.66 km/s per Mpc (Planck 2018).
Comoving distance
How far a galaxy is now, along the expanding grid of space. It adds up the expansion rate over the light's journey, so far away it falls below Hubble's straight line.
Why it matters Each point in the map sits at this distance.
Light-travel time
How long ago the light we see left the galaxy: 0.33 billion years for Coma, 2.5 billion at z = 0.2. The galaxy has moved on since, so it is not its distance divided by the speed of light.
Mpc
A megaparsec: 3.26 million light-years, about 30 times the Milky Way's width.
Cosmic web
The pattern galaxies make on the largest scales: filaments and walls with clusters where they cross, round voids that are nearly empty.
Why it matters Gravity grew it from tiny ripples in the early Universe, so its shape tests how gravity and dark matter work.
Void
A region with far fewer galaxies than average, tens of Mpc across, such as the Boötes void. In the density layer, cells with under a fifth of the expected galaxies.
Survey footprint
The part of the sky SDSS measured: about 8300 square degrees, a fifth of the sky. Outside it the map is empty because nobody looked, not because there is nothing.
Why it matters It tells an empty wedge from a void.
Fingers of God
Clusters look stretched along the line of sight because galaxies orbiting inside them add their own speed, hundreds of km/s, to the expansion's redshift.
Laniakea
Our home supercluster as Tully et al. (2014) drew it: the basin whose galaxies all drift towards the Great Attractor on top of the expansion. Hawaiian for "immense heaven".
Peculiar velocity
A galaxy's own motion on top of the expansion, pulled by the matter round it. Cosmicflows-4 finds it by measuring distances without redshift (Tully–Fisher, supernovae) and subtracting Hubble's law.
Why it matters The flow lines follow these motions, mapped into a 3D field.
Supergalactic plane
The flat sheet most nearby clusters lie in, the equator of the coordinates the map uses. The 100 Mpc rings sit in it, with its pole up.
g − r colour
A galaxy's brightness in green light minus red, in magnitudes. Above about 0.7 it is red, mostly old stars; below, blue, still forming stars.
Why it matters Red galaxies crowd into clusters, blue ones line the filaments.

All help and questions

The cosmic web

Fly through 623 379 real SDSS galaxies: filaments, walls and voids, Virgo and Coma, and Laniakea's flow lines. See how a redshift becomes a distance.

Drag to look round; scroll or pinch to fly forward. Click the map, then W A S D fly, Q and E sink and rise, the arrows turn. Point at a galaxy for its numbers.Drag to look round; pinch to fly forward or back. Tap a galaxy for its numbers.

Fly to
Show
Colour by
  • Rings every 100 Mpc in the supergalactic plane, the flat sheet the nearby clusters lie in.

Point at a galaxy, or tap one, for its numbers.

Galaxies
Loading the nearest galaxies…
You are this far from the Milky Way
—

How a redshift becomes a distance

Space has expanded while the light travelled, and the light stretched with it: every line in a galaxy's spectrum sits at 1 + z times its wavelength at rest. SDSS measures z by lining up those lines. Move the redshift and watch them slide to the red.

400 nm500 nm600 nm700 nm800 nmAt restAs seenKHHβMgNaHα
  • Lines at rest
  • Lines as seen, × (1 + z)
Speed cz
6,925 km/s
Hubble's law, d = cz / H0 (H0 = 67.66)
102 Mpc
Comoving distance
102 Mpc
0.5% short of Hubble's law
Light-travel time
0.33 billion years

Filaments, walls and voids

Galaxies are not spread evenly. Gravity has pulled them into filaments and walls over 13.8 billion years, with clusters where filaments cross and voids between them. The pattern is the cosmic web. Each point is one galaxy whose redshift SDSS measured from its spectrum, placed at the distance that redshift gives.

Empty wedges and fingers

SDSS looked at about 8300 square degrees, a fifth of the sky, mostly away from the Milky Way's dusty disk. The dark wedges outside that are not voids: nobody measured them. Clusters look stretched towards us because the map uses redshift for distance, and galaxies moving inside a cluster add their own speed to it.

Laniakea

Tully et al. (2014) mapped which way galaxies drift on top of the expansion and drew the basin that drains towards the Great Attractor: Laniakea, Hawaiian for "immense heaven", home to the Milky Way. These lines come from the newer Cosmicflows-4 field (Courtois et al. 2023). In it the Milky Way's basin also takes in Perseus–Pisces, which the 2014 map gave a basin of its own: Virgo, the Great Attractor and Perseus flow with us, Coma does not.

Data and credits

Galaxies: the Sloan Digital Sky Survey DR17 main galaxy sample (Strauss et al. 2002; Abdurro'uf et al. 2022), public domain; SDSS-IV is funded by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science and the participating institutions. Distances and flow: Cosmicflows-4 (Tully et al. 2023, ApJ 944, 94, via CDS VizieR) and its velocity field (Courtois et al. 2023, A&A 670, L15, CC BY 4.0). Laniakea: Tully, Courtois, Hoffman and Pomarède 2014, Nature 513, 71. Distances use Planck 2018.

SDSS DR17Cosmicflows-4 catalogueCF4 velocity fieldLaniakea (Nature, 2014)