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Astro*Dictionary by Michael Erlewine





1 article for "Hubble"

Hubble, Edwin Powell [Astro*Index]

(1889-1953) American astronomer. Born at Marshfield, MO; died at San Marino, CA.

Using the 100-inch telescope at Mount Wilson, he studied various nebulae to determine whether any objects other than the Magellanic clouds lay outside our own galaxy (The Milky Way). In 1924, Hubble was able to resolve individual stars within the Andromeda `nebula', and found that some were Cepheid variables. Using the period-luminosity curve of Shapley and Leavitt, he determined a value for the distance of the Andromeda nebula, finding that it did, indeed, lie beyond our own galaxy. At the suggestion of Shapley, such objects are now called galaxies, and we now refer to this first grouping as the Andromeda Galaxy. In 1929, Hubble analyzed the radial velocities of the galaxies (which had been measured by Slipher), and showed that they were all receding from us at velocities proportional to their distance. This observation is best explained by supposing that the universe is expanding, as Sitter had already suggested. And, at some vast distance from us, the velocity of recession should attain the speed of light, at which distance light would no longer reach us; objects might well exist beyond that point, but we could never know of them. Thus, we may speak of this distance as the Hubble radius, which represents the size of an effective sphere which contains that part of the universe which we can come to know; this radius has been estimated at 13 billion LYs (light-years). Reversing the expanding universe would bring all the galaxies together at the moment when the "big bang" occurred. Hubble estimated the time to be about 2 billion years ago. (Baade would later revise this number to at least 3 billion years.)

See also:
♦ Period-luminosity Relation ♦ Radial Velocity ♦ Light, Velocity of ♦ Shapley, Harlow ♦ Baade, Walter ♦ Leavitt, Henrietta Swan ♦ Slipher, Vesto Melvin ♦ Sitter, Willem de


Astro*Index Copyright © 1997 Michael Erlewine