Other Galaxies and Active Galaxies

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Using large telescopes you can see clouds of dust and gas inside the Galaxy. You can also see other peculiar milky nebulae scattered among the stars. Some of these milky nebulae have spiral shapes to them and others look like squashed spheres or tortured messes of material. Three of the milky nebulae are visible as fuzzy patches to the naked eye: one is in the constellation Andromeda and two others (called the Large and Small Magellanic Clouds after the first European explorer to see them, Ferdinand Magellan) are in the southern sky in the constellations Mensa and Hydrus.

Edwin Hubble
Edwin Hubble (courtesy of Edwin Hubble Papers, The Huntington Library, San Marino, CA)
Milton Humason
Milton Humason (courtesy of Observatories of the Carnegie Institution for Science Collection at the Huntington Library, San Marino, CA)

Work by Edwin Hubble (lived 1889--1953) and Milton Humason (lived 1891--1972) in the 1920s established that each of the spiral nebulae was another huge star system, called a galaxy (from the Greek ``galactos'', meaning ``milk''), outside our own galaxy. Telescopes of sufficient size to have the needed resolution to see individual stars in the other galaxies were used by Hubble and Humason to measure the distances to the galaxies. This chapter covers the galactic systems outside our own and a peculiar group of galaxies that produce a large amount of energy in their centers. The vocabulary terms are in boldface.

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last updated: August 27, 2019

Is this page a copy of Strobel's Astronomy Notes?

Author of original content: Nick Strobel