Milky Way Galaxy

Table of Contents

Introduction & Top Questions
Major components of the Galaxy
- Star clusters and stellar associations
  - Globular clusters
  - Open clusters
  - Stellar associations
  - Moving groups
- Emission nebulae
- Planetary nebulae
- Supernova remnants
- Dust clouds
- The general interstellar medium
- Companion galaxies
Star populations and movement
- Stars and stellar populations
  - Principal population types
  - The stellar luminosity function
- Density distribution
  - The stellar density near the Sun
  - Density distribution of various types of stars
  - Variations in the stellar density
  - Variation of star density with z distances
- Stellar motions
  - Proper motions
  - Radial velocities
  - Space motions
  - High-velocity stars
- Solar motion
  - Solar motion calculations from radial velocities
  - Solar motion calculations from proper motions
  - Solar motion calculations from space motions
  - Solar motion solutions
The structure and dynamics of the Milky Way Galaxy
- Size
- Structure of the spiral system
  - The nucleus
  - The central bulge
  - The disk
  - The spiral arms
  - The spherical component
  - The massive halo
- Magnetic field
- Rotation
- Mass

References & Edit History Related Topics

Images & Videos

For Students

Milky Way Galaxy summary

Milky Way Galaxy

Q: Why is it called the Milky Way Galaxy?

The Milky Way Galaxy takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth.

Q: How big is the Milky Way Galaxy?

The first reliable measurement of the size of the Milky Way Galaxy was made in 1917 by American astronomer Harlow Shapley . Assuming that the globular clusters outlined the Galaxy, he determined that it has a diameter of about 100,000 light-years. His values have held up remarkably well over the years.

Q: Is Earth in the centre of the Milky Way Galaxy?

The solar system is about 30,000 light-years from the centre of the Milky Way Galaxy. The Galaxy itself is thought to be about 100,000 light-years in diameter.

astronomy

Also known as: The Galaxy

Written by Paul W. Hodge

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Apr 11, 2025 • Article History

Why is it called the Milky Way Galaxy?

How big is the Milky Way Galaxy?

Is Earth in the centre of the Milky Way Galaxy?

News •

Astronomers found something very strange at the core of our Milky Way galaxy • Apr. 10, 2025, 11:59 AM ET (Earth.com)

It gave us the best map of the Milky Way. Now the Gaia spacecraft is orbiting into retirement • Apr. 1, 2025, 6:34 AM ET (CBC)

Gaia to Shut Down After More Than a Decade of Mapping the Milky Way • Mar. 27, 2025, 2:49 AM ET (New York Times)

Supermassive Black Hole Discovery Hints at Deadly Future for Milky Way • Mar. 25, 2025, 1:10 AM ET (Newsweek)

High-school student accidentally discovers black hole 'light echo' twice as wide as the Milky Way • Mar. 22, 2025, 8:44 AM ET (Live Science)

Milky Way Galaxy, large spiral system consisting of several hundred billion stars, one of which is the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth. Although Earth lies well within the Milky Way Galaxy (sometimes simply called the Galaxy), astronomers do not have as complete an understanding of its nature as they do of some external star systems. A thick layer of interstellar dust obscures much of the Galaxy from scrutiny by optical telescopes, and astronomers can determine its large-scale structure ...(100 of 13945 words)

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