Sgr A* — Accretion Disk
Bulge — Old K/M Giants
Spiral Arms — Young OB Stars
HII Regions — H-alpha
Nebulae — Gas Clouds
Globular Clusters
☀ Solar System (You Are Here)
Dark Matter Halo

type SBbc Barred Spiral

center Sgr A* — 4×10⁶ M☉

diameter ~100,000 ly (~30.7 kpc)

bar length ~27,000 ly (~8.3 kpc)

Sun distance ~26,000 ly from center

rotation v_c ≈ 220 km/s flat

stars ~200–400 billion

age ~13.6 Gyr

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Perseus Arm
Norma Arm
Sagittarius Arm
Orion Spur ☀
☀ You Are Here
Spiral Arms
4 major + spurs
Perseus, Norma, Sagittarius, Crux-Centaurus. Sun sits in Orion Spur between Perseus & Sagittarius.
Nebulae
Gas & Dust Clouds
HII regions glow red. Planetary nebulae show purple, blue, teal. ~6,000 catalogued.
Central Bar
~27,000 ly long
Barred spiral SBbc. Bar funnels gas inward. Drives spiral density waves. Angle ~44° to Sun–center line.
Dark Matter
R > 80 kly
~85% of galaxy mass. Spherical halo. Explains flat rotation curve out to 100+ kly.
1.0×
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