Milky Way Galaxy
Our home spiral galaxy containing hundreds of billions of stars.
Overview
The Milky Way is a barred spiral galaxy containing 100–400 billion stars, a supermassive black hole (Sagittarius A*), and our solar system in the Orion Arm.
Why It Matters
Our galaxy is our cosmic address. Understanding its structure reveals how galaxies form, evolve, and interact with dark matter.
Scientific Explanation
The Milky Way spans ~100,000 light-years with a central bar and four major spiral arms. Stars in the disk orbit every ~230 million years. Gaia mapped over a billion stars, revolutionizing our 3D model. Dark matter halo dominates mass but emits no light.
Historical Background
Until 1920, many thought the Milky Way was the entire universe (Great Debate). Hubble proved Andromeda was external. Radio maps revealed spiral structure obscured by dust.
Visual Explanation
Face-on: central bulge, spiral arms, bar. Edge-on: thin disk, thick halo, dust lane. We sit ~26,000 ly from center, orbiting at ~220 km/s.
Key Discoveries
- ✦ Shapley locates galactic center in Sagittarius (1918)
- ✦ Hubble confirms Milky Way is one galaxy among many
- ✦ Gaia creates precision 3D star map
- ✦ Event Horizon Telescope images Sagittarius A* (2022)
Important Astronomers
Reflection Prompt
You are made of stardust from earlier generations of Milky Way stars. What does galactic citizenship mean to you?
Write in Journal →