Types of Galaxies
Galaxies come in a handful of basic shapes — graceful spirals, smooth ellipticals, in-between lenticulars, and chaotic irregulars. A century ago Edwin Hubble sorted them into a diagram shaped like a tuning fork, and it's still how we classify them today. Learn the four families and you can name almost any galaxy at a glance.
Image: NASA/ESA and the Hubble Heritage Team (STScI/AURA). The Sombrero (M104) — a spiral galaxy seen almost edge-on, showing the flat disk and central bulge that define the spiral family.
The Hubble tuning fork
In 1926, Hubble arranged galaxies by shape into a branching diagram. On the handle sit the round-to-oval ellipticals; where the handle splits, the two prongs are the spirals — ordinary spirals on one prong, barred spirals on the other — with the disk-but-no-arms lenticulars at the junction. The messy irregulars don't fit the fork at all. Hubble thought it might show how galaxies evolve; it doesn't (galaxies don't slide along it as they age), but as a way to sort them by appearance, it has never been bettered.
Diagram by Michael Paycer. Our own Milky Way is a barred spiral — an "SBc" on the lower prong.
How to tell them apart
Spiral galaxies
A flat, rotating disk with a central bulge and graceful arms of gas, dust, and young blue stars — the classic pinwheel. Still actively forming stars. About two-thirds have a straight "bar" of stars through the center (barred spirals). Examples: the Whirlpool, the Milky Way, Andromeda.
Elliptical galaxies
Smooth, featureless balls of old red-yellow stars, from nearly spherical to football-shaped, with little gas and almost no new star formation — galactic retirees. The largest galaxies in the universe are giant ellipticals at the centers of galaxy clusters, built by mergers.
Lenticular galaxies
The in-betweens (type S0): they have a disk and bulge like a spiral, but no spiral arms and little gas, like an elliptical. Often seen edge-on as a bright lens with a dust line — the Spindle Galaxy is a striking example.
Irregular galaxies
No clear shape at all — chaotic blobs of gas and vigorous star formation, often small and often distorted by the gravity of a larger neighbor. The Milky Way's own companions, the Magellanic Clouds, are irregulars visible from the Southern Hemisphere.
What the shapes look like to you
Honest expectations: through a backyard telescope, a galaxy's type is usually hard to make out, because you're seeing a faint grey glow, not the crisp photo. Still, some structure survives. Elliptical galaxies look like fuzzy, featureless ovals — easy to find, but frankly a little dull visually (they're all core, no detail). Spirals are the prize: a bright core with a hazy disk, and under dark skies with enough aperture, hints of the arms and dust lanes emerge — the Whirlpool's two arms are famously glimpsable in a good scope. Edge-on spirals and lenticulars like the Sombrero are the most satisfying, because their slivered shape and dust lane read clearly even when faint. The rule for all of them: aperture and dark skies beat magnification. See the telescope guide and how to observe.
The Milky Way · Galaxy Collisions · Whirlpool · Sombrero · Galaxies Hub · Telescopes · Glossary
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