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April 15, 2024

Backyard Astronomy: Galaxies

By Cheryl Haimann

A while back, this column reported on the Hubble Telescope's "You Decide" program, where visitors could vote for the next object to be viewed by the space telescope. The winning object, a trio of galaxies called Arp 274, was photographed earlier this month.

It's only fitting that a group of galaxies won the vote, because galaxies are how astronomer Edwin Hubble, for whom the telescope is named, rose to prominence.

Until the early 1920s, if you said "galaxy", you would be referring to our own galaxy, the Milky Way. As far as anyone knew, that was the sum total of the universe. Astronomers understood that some of the fuzzy objects, or nebulae, that they could see through telescopes, such as the Great Orion Nebula (M42), were part of our own galaxy.

Other nebulae, though, were more perplexing. Some had a spiral shape, and those were particularly intriguing to Hubble, a lawyer-turned-astronomer who was working at the Mount Wilson observatory in California. Using the new 100-inch Hooker Telescope at Mount Wilson, Hubble was able to observe stars in several of the spiral nebulae.

By taking measurements on some of these stars, Hubble determined that the spiral nebulae were millions of light years away, far beyond the boundaries of the Milky Way. The spiral nebulae were not nebulae at all. They were galaxies, just like our own, and the universe was greatly more vast than anyone knew.

The recently photographed Arp 274 is one of the objects in Halton Arp's Atlas of Peculiar Galaxies, a listing of galaxies that are not spiral or elliptical in shape. Hubble calculated the distance to galaxies using redshift, the light wave equivalent of the Doppler effect you hear when a fire truck zooms by. Arp's study of irregular galaxies, and the area around them, suggests that redshift might not be accurate in every situation.

This notion, if proven, would turn our understanding of the universe on its ear, just as Hubble's conclusions did 85 years ago.


Cool Thing of the Week: Astronomy Day May 2, 2009

This year's first Astronomy Day occurs on May 2. Planetariums, science museums, and local astronomy clubs will have special events. Many organizations will offer public viewing on that night, so anyone can take a look through a telescope. In addition to the link above, check here for planetariums holding special events, and also check your local newspaper, radio, and television stations for events happening in your area.


Backyard Astronomy updates are available on Twitter!

Article © Cheryl Haimann. All rights reserved.
Published on 2009-04-27
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