Local Group · Deep Field · Cosmology

Galaxy
AtlasThree worlds beyond our own

From the spiral arms we call home to the graceful Triangulum and the vast Armada cluster — three galaxies that anchor our understanding of the universe's structure.

⊛ Milky Way △ Triangulum ⊕ Armada Galaxy
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200B
Stars
Milky Way population
40B
Stars
Triangulum Galaxy
1,000+
Galaxies
Armada cluster members
Spitzer / ESA · Illustration
Milky Way — barred spiral · artist's impression
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Barred Spiral Galaxy
The Milky
Way
Our home in the cosmos
The Milky Way is a barred spiral galaxy containing between 200 and 400 billion stars, spanning roughly 100,000 light-years across. We sit about 26,000 light-years from the galactic centre, inside one of the minor spiral arms — the Orion Arm.

At its heart lies Sagittarius A*, a supermassive black hole of about 4 million solar masses. The galaxy is surrounded by a diffuse dark matter halo roughly ten times larger than the visible disc. Our solar system takes approximately 225 million years — one "galactic year" — to orbit the centre.
Diameter
~100,000 ly
Stars
200–400 billion
Central black hole
Sgr A* · 4M M☉
Galactic year
225 million yrs
Type
SBbc barred spiral
Sun's position
Orion Arm · 26kly
Barred SpiralSagittarius A* Dark Matter HaloLocal GroupOrion Arm
Hubble / ESA · Illustration
Triangulum — M33 · face-on spiral · ~2.73 Mly
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Spiral Galaxy · M33
Triangulum
Galaxy
The farthest naked-eye object
Messier 33, the Triangulum Galaxy, is the third-largest member of the Local Group — the small cluster of galaxies that includes the Milky Way and Andromeda. Located roughly 2.73 million light-years away in the constellation Triangulum, it is the most distant object visible to the naked eye under perfect dark skies.

Unlike our galaxy, Triangulum has no prominent central bar, appearing as a pure spiral face-on. It contains about 40 billion stars and is unusually rich in star-forming regions — its HII nebulae include NGC 604, one of the largest known stellar nurseries, dwarfing our own Orion Nebula by 40 times.
Distance
2.73 million ly
Diameter
~60,000 ly
Stars
~40 billion
Largest nebula
NGC 604
Type
SA(s)cd spiral
Group
Local Group #3
Unbarred SpiralM33 NGC 604Local GroupNaked Eye
Chandra / NASA · Illustration
Armada Galaxy — galaxy group · wide-field illustration
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Galaxy Cluster
Armada
Galaxy
A fleet of galaxies in formation
The "Armada Galaxy" refers to a compact galaxy group or cluster — a gravitationally bound ensemble of hundreds to thousands of individual galaxies moving together through deep space. Like a fleet of ships, the member galaxies orbit a common centre of mass, interacting through gravity, triggering star formation, and occasionally merging.

Galaxy clusters are the largest gravitationally bound structures in the universe. They are dominated by invisible dark matter (roughly 85% of total mass), with the visible galaxies and hot X-ray-emitting gas making up the rest. Studying clusters like this reveals how the cosmic web of large-scale structure formed after the Big Bang.
Members
1,000+ galaxies
Dark matter
~85% of total mass
Intracluster gas
Hot X-ray plasma
Structure type
Galaxy cluster
Interactions
Mergers · tidal
Cosmic role
Large-scale tracer
Galaxy ClusterDark Matter X-ray PlasmaGravitational LensingCosmic Web