Celestial Tour: Discovering Galaxies—Beyond the Milky Way

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In 1923, astronomer Edwin Hubble aimed the world's largest telescope--a newly built 100-inch telescope atop California's Mount Wilson--at the Great Andromeda Nebula.

Produced by the Space Telescope Science Institute’s Office of Public Outreach.

All images, illustrations, and videos courtesy of NASA, ESA, and STScI except:
  • Milky Way panoramas courtesy of ESO/Y. Beletsky and ESO/Bruno Gilli
  • Photos of Edwin Hubble courtesy of Huntington Library
  • Andromeda Galaxy image courtesy of Bill Schoening, Vanessa Harvey/REU program/NOAO/AURA/NSF
  •  Photo of Henrietta Leavitt courtesy of American Institute of Physics, Emilio Segrè Visual Archives
  • M33, M94, NGC 55, M49, and M84 images courtesy of NOAO/AURA/NSF
  • NGC 6822 image courtesy of Local Group Galaxies Survey Team/NOAO/AURA/NSF
  • NGC 1232 image courtesy of ESO/P. Grosbøl
  • NGC 4449 image courtesy of Digital Sky Survey/AURA
  • NGC 1300 image courtesy of Hillary Mathis/NOAO/AURA/NSF
  • Small Magellanic Cloud image courtesy of F. Winkler/Middlebury College, the MCELS Team, and NOAO/AURA/NSF
  • NGC 55 color image courtesy of T. A. Rector/NOAO/AURA/NSF
  • Written by Vanessa Thomas
  • Designed by John Godfrey 
  • Music courtesy of Association Production Music


 Title, Discovering Galaxies. The text warps and waves. 

Black space is filled with distant stars and streaks of light. Text, Our universe is full of beautiful, dynamic, wild-looking, and enormous galaxies. A spiraling disk-shaped glowing cloud comes into view. Red and white stars twinkle. Text,, But just a century ago, nobody knew. 

The glowing Milky Way along with billions of stars light up the sky with dark mountains silhouetted in the foreground. Text, Many believed our galaxy, the Milky Way, was all there was, that nothing existed beyond. Yet, there were faint, fuzzy patches in the sky called nebulae, Latin for clouds. 

A rotating dotted circular line is drawn around a white streak far to the left of the Milky Way. Text, Some people wondered whether these nebulae were other galaxies, like our own, located very far away. 

Historic photo, a man looks through and adjusts a giant telescope, Text, In 1923, astronomer Edwin Hubble aimed the world's largest telescope, a newly built 100-inch telescope atop California's Mount Wilson, at the Great Andromeda Nebula. 

A white, glowing cloudy disk comes into view. Text, In it, he found a star that brightened, dimmed, and brightened again over the course of a month. The blinking star is highlighted with a rotating yellow line on the outer edge of the nebula. It was a cosmological jackpot, a Cepheid variable star. 

Historical photo, a woman studies a printed sheet. Text, About a decade earlier, while studying thousands of variable stars, stars that change in brightness, Harvard Observatory's Henrietta Leavitt had discovered a remarkable quality of Cepheid variables. 

Bright Cepheids pulsate slower than dim ones do. A side by side comparison shows a dim Cepheid star next to a bright Cepheid star. The dim star pulsates quickly. The bright star pulsates slowly. 

Text, This solved a problem. 

Like light bulbs, stars have different wattages. A dimmer lightbulb sits next to a brighter lightbulb. 

The brighter bulb moves away into the distance across a grid in perspective until it matches the brightness of the dim bulb in the foreground. Text, When you see a faint star in the night sky, how do you know whether it is truly dim and nearby, or bright but far away? 

A Cepheid star in the Andromeda Nebula blinks slowly on the outer edge. Thanks to Henrietta Leavitt's discovery, Edwin Hubble could figure out how bright the Cepheid in Andromeda Nebula really was by timing how quickly the star changed brightness. Historic photo, Edwin Hubble examines images. 

Text, This Cepheid had a slow pulse, which meant it was a bright star very far away, much too far, Hubble calculated, to belong to our galaxy. 

The Andromeda Nebula had to be another galaxy far beyond our own. 

We move closer to the glowing white center of the Andromeda Nebula. 

Today, we call it the Andromeda Galaxy. 

A bright white galaxy filled with stars is patchy white in the center with sections spiraling out. Text, Edwin Hubble calculated the distance to other nebulae, proving that they too were far-off galaxies. The nebula rotates as we move away from it. 

Another round galaxy made up of millions of stars is brighter in the center. Text, It was suddenly clear, our galaxy is not alone. 

Another spiral galaxy has a solid white section in the middle with less dense stars spinning around the perimeter. Text, With the powerful 100-inch telescope, Edwin Hubble could also see that these newly identified galaxies came in a variety of shapes. 

Some galaxies are wound tight, with spiral arms that wrap closely around their cores. 

The bright galaxy slowly rotates clockwise. 

A galaxy has a small bright center with long filmy arms spiraling out. Text, Other spirals appear more relaxed, with arms spread out. 

A long cigar-shaped galaxy with a bright section on the left side. Text, Some galaxies appear long and thin. 

A galaxy has a bright white oval center with a sprinkling of stars surrounding it that fade out. Text, Others are round or oval-shaped with no arms at all. 

A glowing galaxy has a spatter of bright sections generally box-shaped. Text, There are even some galaxies that have no organized shape, they just look like messy blobs. 

A wishbone-shaped illustration shows the different shapes of galaxies starting with simple circles and ovals and branching into two arms of three variations of spiral shapes. Text, Hubble classified galaxies by their shape into categories that astronomer still use today. 

Edwin Hubble's work changed our view of the universe forever. A gold galaxy is next to a white galaxy 

Text, No longer was the Milky Way the sole galactic member of the universe. 

As we move away, different shaped galaxies appear as circles and streaks in dark space. 

Text, We know now that our galaxy is one of billions. Today, a space telescope named after Hubble continues to reveal that the universe is even more vast and full of galaxies than perhaps Hubble himself could have ever imagined. 

A model of the Hubble telescope floats in space. Space condenses to show millions of stars and galaxies.