Walk Edwin Hubble's "tuning fork" diagram in 3D: morph a galaxy from a round elliptical through the most flattened ellipticals, then branch into a normal spiral or a barred spiral and slide from a large tightly-wound bulge down to a small loosely-wound one - the same classification system astronomers still use today.
Hubble Tuning Fork 3D Explorer
Morph a 3D galaxy through Edwin Hubble's tuning-fork classification: round it out from E0 to the most flattened ellipticals at E7, cross into the lenticular transition class, then branch into a normal spiral or a barred spiral and slide the bulge and arm-winding from a tightly-wound "a" down to a loosely-wound "c" - the same system professional astronomers still use to sort galaxies today.
Twelve buttons walk the fork rung by rung, a Normal/Barred toggle swaps which of the two parallel branches you are on, and a "Real-galaxy challenge" picks a real, named galaxy and gives you a clue - set your own guess with the buttons, then press Reveal to see its real classification and the sourced fact behind it.
- Eight elliptical buttons (E0-E7) morph a point-cloud "ball of old stars" from round to the most flattened shape actually observed, following the real ellipticity formula e = 1-(b/a)
- S0 button shows the lenticular transition class: a disk and a bulge like a spiral, but no visible arms
- a/b/c buttons scrub bulge size and spiral-arm winding tightness on whichever branch is selected - large bulge and tight arms at "a", small bulge and loose arms at "c"
- Normal spiral (S) vs Barred spiral (SB) toggle adds or removes the central bar that about two-thirds of real spiral galaxies - including the Milky Way and Andromeda - actually have
- "Walk the fork" auto-steps through all twelve rungs hands-free
- "Show irregulars" reveals a lumpy, off-to-the-side shape for the class Hubble deliberately left OUT of the fork entirely
- "Real-galaxy challenge" cycles through seven real, named galaxies (M87, NGC 2865, NGC 4886, the Sombrero Galaxy, the Pinwheel Galaxy, Andromeda, and the Milky Way) with a clue and a sourced reveal
- Drag to orbit, scroll or pinch to zoom; runs fully in the browser with the vendored three.js engine - no account, no upload; your last setting is remembered on your device
| Rung | Branch | What defines it |
|---|---|---|
| E0-E7 | Elliptical | Ellipticity e = 1-(b/a), number = round(10e). No gas, no dust, no ongoing star formation |
| S0 / SB0 | Lenticular | Disk + bulge like a spiral, but no visible arms - the transition class added in 1936 |
| Sa / SBa | Spiral / barred spiral | Large central bulge, tightly-wound arms |
| Sb / SBb | Spiral / barred spiral | Medium bulge, medium-wound arms |
| Sc / SBc | Spiral / barred spiral | Small bulge, loosely-wound, clumpier arms |
Why a fork, not a line: two branches for the same bulge-to-arm story
Hubble split spirals into two parallel prongs because roughly a third to about two-thirds of them (depending on the survey) carry a bar of stars, gas, and dust cutting straight through the central bulge, with the spiral arms springing from the bar's ends rather than from the bulge itself. NASA Science puts it plainly: both the Milky Way and Andromeda - our nearest large galactic neighbor - are barred spirals, "which make up two-thirds of the group." Both prongs still run through the same a/b/c bulge-size and arm-tightness story; the bar is the only structural difference the fork records.
A system built on a wrong idea that still works
When Hubble built this diagram in the 1920s he thought galaxies evolved from ellipticals into spirals over time - which is why "early type" still means elliptical and "late type" still means a loosely-wound spiral in astronomy papers today. That evolutionary idea turned out to be wrong; ellipticals and spirals are not two stages of the same galaxy's life. What survived is the classification itself, because the tuning fork actually sorts galaxies by something real and physical: how fast they rotate. Spirals spin fast; ellipticals barely rotate at all, or not in any organized way.
For a single spiral galaxy's own internal structure and scale - not the classification system that sorts every galaxy type - see the Galaxy 3D Simulator. This page instead teaches the taxonomy: which shape puts a galaxy on which branch, and why.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached, and nothing about your visit is sent to a server.
This is an educational approximation, not a galaxy-formation or light-profile simulator: the elliptical shapes follow the real ellipticity formula, and the spiral/barred-spiral bulge-and-arm-tightness trend follows the real documented "a tight/large to c loose/small" pattern - neither is fit to any one real galaxy's actual measured surface photometry. The named real-galaxy classifications in the "Real-galaxy challenge" are the commonly-cited values for each (sources vary slightly on exact numbered subtypes for some, such as M87).
Frequently Asked Questions
What does E0 through E7 mean?
It is the elliptical-galaxy flattening scale: ellipticity e = 1-(b/a), where a and b are the apparent major and minor axis. The classification number is e multiplied by 10 and rounded. E0 looks nearly circular; E7 is the most flattened commonly observed - real ellipticals flatter than about that are not seen, because they could not hold together as a simple shape.
What is a lenticular (S0) galaxy?
A disk and a central bulge like a spiral galaxy, but with no visible spiral arms and little to no gas or dust. It sits at the fork's joint, between ellipticals and spirals, and was added to Hubble's original scheme in 1936.
What do "a", "b", and "c" mean on the spiral branches?
They describe bulge size and spiral-arm winding tightness. "a" (Sa or SBa) has a large central bulge with tightly-wound arms; "c" (Sc or SBc) has a small bulge with loosely-wound, clumpier arms; "b" sits in between.
What is the difference between a normal spiral (S) and a barred spiral (SB)?
A barred spiral has a straight bar of stars, gas, and dust cutting through its central bulge, with the spiral arms springing from the bar's ends. Per NASA Science, about two-thirds of spiral galaxies - including the Milky Way and Andromeda - are barred.
Is the Milky Way a normal spiral or a barred spiral?
A barred spiral, commonly cited around SBbc or SBc - the same category as Andromeda, our nearest large galactic neighbor. See the Milky Way Map 3D Explorer for the Milky Way's own internal structure and scale.
What is M87 and why is it famous?
A giant elliptical galaxy at the heart of the Virgo galaxy cluster, often cited around E0-E1. Its supermassive black hole was the subject of the first-ever image of a black hole, released by the Event Horizon Telescope collaboration in 2019.
Does the fork cover every galaxy shape?
No. Hubble's original scheme deliberately excludes irregular galaxies - ones with no clean elliptical or spiral shape. Press "Show irregulars (beyond the fork)" to see NASA's own example, NGC 5264, shown off to the side because it does not belong on the fork at all.
Did Hubble get the reason the classification works correct?
No - and that is a genuinely interesting wrinkle. Hubble originally thought ellipticals evolved into spirals over time, which is why astronomers still call ellipticals "early type" and loosely-wound spirals "late type" today. That evolutionary idea was wrong. What actually makes the fork meaningful is that it sorts galaxies by real rotation speed: spirals spin fast, ellipticals barely rotate.
Is this the same as the Galaxy 3D Simulator?
No. The Galaxy 3D Simulator shows one spiral galaxy's own internal structure and scale in detail. This page instead teaches the classification system used to sort every galaxy - elliptical, lenticular, normal spiral, or barred spiral - into its type.
Is this a real galaxy-formation simulation?
No. It is an educational approximation: the elliptical shapes follow the real ellipticity formula, and the spiral/barred-spiral bulge-and-arm trend follows the real documented pattern, but neither is fit to any one real galaxy's measured surface photometry. The named real-galaxy classifications are the commonly-cited values for each.