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Edwin Hubble: Discoveries, Theory & Accomplishments

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  • 0:02 Discoveries
  • 1:03 Theory
  • 2:51 Accomplishments
  • 3:13 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Edwin Powell Hubble was an American astronomer and pioneer of observational cosmology. His observations and discoveries led to a change in the understanding of the universe. This lesson looks at his accomplishments.

Discoveries

In the early 20th century, it was believed by most that the Milky Way was in fact the entire universe. In 1924, Hubble used the reflecting telescope at the Mount Wilson Observatory and began observing nebulae. His observations and calculations led to the realization that these nebulae were, in fact, hundreds of thousands of light-years away from the Milky Way and far larger than the diameter of the Milky Way.

These observations led Hubble to speculate that these nebulae must be located outside the Milky Way and that the universe must be larger than just the Milky Way. In 1924, the American Astronomical Society announced the discovery at an academic conference where it was widely accepted. After continued observations, Hubble began classifying galaxies into categories by their appearance, which would become known as the Hubble classification.

Theory

By 1929, Hubble had measured the distance to over 20 galaxies using spectral analysis on the distant objects. Hubble noticed that the spectral lines were red-shifted, meaning they were moving further away. In fact, Hubble noticed the farther the galaxy was, the greater the red-shift was, meaning that the farther away a galaxy was, the faster away it was moving.

Continuing his observations, Hubble noticed the velocity at which galaxies were moving away from us divided by the galaxy distance was a constant, meaning there is a linear relationship between the two. The velocity of galaxies divided by the distance of galaxies is known as the Hubble constant. Hubble formulated his observations into an equation that would become known as Hubble's law, which is:

V = Hsub0 D

where:

  • H is Hubble's constant
  • V is velocity that objects are moving away in km/s (kilometers per second)
  • D is the distance from the observer (usually Earth) to the object being observed

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