---
title: "Edwin Hubble | Intro to Astronomy"
description: "Edwin Hubble showed that many nebulae are separate galaxies and that their redshift reveals an expanding universe in Intro to Astronomy."
canonical: "https://fiveable.me/intro-astronomy/key-terms/edwin-hubble"
type: "key-term"
subject: "Intro to Astronomy"
unit: "Unit 29"
---

# Edwin Hubble | Intro to Astronomy

## Definition

Edwin Hubble was the astronomer who showed that galaxies exist beyond the Milky Way and that the universe is expanding. In Intro to Astronomy, his work connects distance, redshift, and the scale of the cosmos.

## What It Is

Edwin Hubble is the astronomer whose observations changed Intro to Astronomy from a Milky Way-centered view to a universe full of galaxies. He is best known for two linked discoveries: some fuzzy “nebulae” were actually separate galaxies, and more distant galaxies show greater redshift, which points to an expanding universe.

The first part of Hubble’s work solved a huge distance problem. Astronomers had seen spiral-looking objects like Andromeda for years, but they did not know whether those objects were inside the Milky Way or far outside it. Hubble used Cepheid variable stars in Andromeda to measure its distance. Because Cepheids have a known relationship between their brightness changes and their true luminosity, they work like standard candles.

Once Hubble could estimate the distance, Andromeda was clearly too far away to be part of the Milky Way. That meant the universe was much larger than people had thought. What used to be called a “nebula” could actually be a galaxy, a separate island of stars, gas, and dust.

Hubble then compared galaxy distances with their spectra. He found that many galaxies have redshifted light, meaning their spectral lines are shifted toward longer wavelengths. In astronomy, that usually means the object is moving away from us. The bigger the distance, the larger the redshift, which became Hubble’s law, written as v = H0d.

That relationship does not mean galaxies are flying through space from a single explosion point like shrapnel. Instead, space itself is expanding, so distant galaxies recede from one another as the universe grows. That is why Hubble’s name shows up in topics like the expanding universe, the age of the universe, and models of cosmic evolution.

A useful way to remember Hubble is this: he did not just observe galaxies, he gave astronomy a measuring stick. First he proved that some “nebulae” were outside the Milky Way, then he connected distance to redshift and helped turn expansion from a guess into a measured pattern.

## Why It Matters

Hubble matters because nearly every big picture astronomy topic after galaxies depends on the shift he helped prove. If you are studying the expanding universe, the age of the universe, or why distant galaxies look redshifted, you are using Hubble’s observations.

His work also shows how astronomy actually works as a science. You do not just look at something and guess its distance. You combine a distance indicator, like Cepheid variable stars, with spectral evidence, like redshift, and then build a model from the data. That pattern shows up again and again in astronomy labs and problem sets.

Hubble also changed the scale of the universe. Before his measurements, the Milky Way was often treated as the whole universe or nearly the whole universe. After his work, students have to think in terms of galaxies, clusters, and cosmic expansion, not just stars inside our own galaxy.

His name also comes up when you interpret what a graph means. A relationship between distance and recessional velocity is not just a random chart, it is one of the core pieces of evidence for cosmology. If you can explain Hubble’s contribution, you can explain why modern astronomy treats the universe as dynamic instead of static.

## Connections

### Redshift

Hubble’s galaxy observations used redshift as the velocity clue. When a galaxy’s spectral lines shift toward longer wavelengths, that usually means it is moving away from us. Hubble connected that shift with distance, which is why redshift is one of the main pieces of evidence for cosmic expansion in Intro to Astronomy.

### [Cepheid Variable Stars](/intro-astronomy/key-terms/cepheid-variable-stars)

Cepheid variables gave Hubble the distance measurements he needed. Their regular brightness changes let astronomers estimate how far away a galaxy is by comparing observed brightness to true luminosity. Without Cepheids, Hubble could not have shown that Andromeda and similar objects were outside the Milky Way.

### Extragalactic Nebulae

This is the older label for objects Hubble proved were separate galaxies. The term matters because many early astronomers thought these fuzzy patches were clouds inside the Milky Way. Hubble’s work changed that interpretation and helped separate true galaxies from objects that only looked small or blurry through early telescopes.

### [Cosmic Perspective](/intro-astronomy/key-terms/cosmic-perspective)

Hubble’s discoveries expand the scale of the cosmic perspective. Once you know the Milky Way is just one galaxy among many, the universe stops feeling like a star field around Earth and starts looking like a huge, evolving system. That shift in scale is a big part of the astronomy mindset.

## On the AP Exam

A quiz question might ask you to identify what Hubble proved from observing Cepheid variables in Andromeda, or to explain why redshift supports an expanding universe. In a short answer, you may need to connect three steps: Hubble measured distance, found that some nebulae were actually galaxies, and then matched increasing redshift with increasing distance.

If you see a graph, data table, or spectrum, use Hubble’s name to describe the pattern, not just the person. For example, if farther galaxies have larger redshifts, you would explain that this is evidence for Hubble’s law and cosmic expansion. In a written response, mention that his work moved astronomy beyond the Milky Way and helped establish the modern model of a growing universe.

## Edwin Hubble vs Copernican Revolution

Both ideas changed humanity’s place in the universe, but they happened at different scales. The Copernican Revolution moved Earth out of the center of the Solar System, while Hubble moved the Milky Way out of the center of the known universe by showing that many nebulae are separate galaxies and that space is expanding.

## Key Takeaways

- Edwin Hubble is the astronomer who proved that many fuzzy nebulae are actually separate galaxies outside the Milky Way.
- He used Cepheid variable stars as standard candles to measure distances to galaxies like Andromeda.
- Hubble’s observations linked galaxy distance with redshift, which became Hubble’s law.
- His work gave strong evidence that the universe is expanding, a foundation of modern cosmology.
- In Intro to Astronomy, Hubble’s name usually shows up whenever you talk about galaxies, distance measurement, or the age and expansion of the universe.

## FAQs

### What is Edwin Hubble in Intro to Astronomy?

Edwin Hubble is the astronomer whose measurements showed that many “nebulae” are actually galaxies beyond the Milky Way. He also found that more distant galaxies have greater redshift, which supports an expanding universe.

### How did Edwin Hubble prove Andromeda was outside the Milky Way?

He identified Cepheid variable stars in Andromeda and used them to calculate its distance. That distance was far too large for Andromeda to be inside the Milky Way, so it had to be a separate galaxy.

### Is Edwin Hubble the same thing as Hubble’s law?

No, Edwin Hubble is the person, and Hubble’s law is the relationship he found between a galaxy’s distance and its recessional velocity. The law is what you use to describe the pattern in the data, not the astronomer himself.

### Why does Edwin Hubble matter for the expanding universe?

Hubble gave astronomers direct evidence that galaxies are moving away from us and that the farther away they are, the faster they recede. That pattern is one of the main reasons astronomers describe the universe as expanding instead of static.

## Related Study Guides

- [29.1 The Age of the Universe](/intro-astronomy/unit-29/1-age-universe/study-guide/LbufKS9hM0PfZEKt)
- [29.2 A Model of the Universe](/intro-astronomy/unit-29/2-model-universe/study-guide/Y2sKjhlgMb27RJqy)
- [26.1 The Discovery of Galaxies](/intro-astronomy/unit-26/1-discovery-galaxies/study-guide/aGPLxqga9CdrfVLm)
- [1.5 Consequences of Light Travel Time](/intro-astronomy/unit-1/5-consequences-light-travel-time/study-guide/cFBxbQVQpndnQmXY)
- [26.5 The Expanding Universe](/intro-astronomy/unit-26/5-expanding-universe/study-guide/m2nF3ZT5zwiDgY60)
- [1.9 A Conclusion and a Beginning](/intro-astronomy/unit-1/9-conclusion-beginning/study-guide/tWNkuM7dp06CBoDu)

## About This Document

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