More to Explore 37
Wright considered that the stars might be spread along the surfaces of a field of giant
bubbles. If we were packed along one of those rings of stars, looking along the ring would
cause us to see more stars than if we looked straight out from it. He then considered the rings
of Saturn and proposed that the stars might be packed into wide rings or a thin disk. If we
were in that disc, it would account for the uneven distribution of stars we saw—even if the
stars were really evenly spaced across that disk.
In 1750 Wright published a book, An Original Theory on New Hypothesis of the Universe, in which he proposed this theory. He was the first to use the word galaxy to describe a
giant cluster of stars. Five years later, famed astronomer and mathematician Immanuel Kant
proposed a similar arrangement of the stars into a giant disk-shaped cluster.
English astronomer William Hershel (born in 1738) read with interest Wright’s theory.
In 1785 Herschel decided to use statistical methods to count the stars. He surely couldn’t count
them all. So he randomly picked 683 small regions of the sky and set about counting the
stars in each region using a 48-inch telescope—considered a giant scope at the time.
Herschel quickly realized that the number of stars per unit area of sky rose steadily as he approached the Milky Way and spiked in regions in the Milky Way. (The number of stars per
unit area of sky reached a minimum in directions at right angles to the Milky Way.)
This made Herschel think of Wright’s and Kant’s theories. Hershel concluded that his
counting results could only be explained if most of the stars were compacted into a
lens-shaped mass and that the sun was buried in this lens. Herschel was the first to add statistical measurement to Wright’s discovery of the existence and shape of galaxies.
Fun Facts: The central galaxy of the Abell 2029 galaxy cluster, 1,070
million light years distant in Virgo, has a diameter of 5,600,000 light
years, 80 times the diameter of our own Milky Way galaxy.
More to Explore
Greenstein, George. Portraits of Discovery: Profiles in Scientific Genius. New York:
John Wiley & Sons, 1997.
Hubbard, Elbert. William Hershel. Whitefish, MT: Kessinger, 2001.
Roan, Carl. The Discovery of the Galaxies. San Francisco: Jackdaw Publications,
2000.
Taschek, Karen. Death Stars, Weird Galaxies, and a Quasar-Spangled Universe. Albuquerque: University of New Mexico Press, 2006.
Whitney, Charles Allen. Discovery of Our Galaxy. Iowa City: Iowa State Press, 1997.