Astronomy

ASTRONOMY

The Big Bang Theory. During the first decades of the twentieth century cosmologists, physicists, and astronomers proposed various theories about the formation of the universe, debating whether the universe was static or dynamic and expanding. In the 1940s astronomer George Gamow and his colleagues at George Washington University proposed a model of the universe developed from Albert Einstein's 1916 theory of relativity and Edwin Hubble's first measurements of distances in galaxies in 1929. Gamow's Big Bang theory hypothesizes that the universe began with the explosion of primeval matter in a state of extreme heat and high density, beginning the ongoing dynamic expansion of the universe. Gamow theorized that primordial matter consisted of neutrons and their decay products—protons and electrons mixed together—in a sea of high-energy radiation. This matter provided the basic ingredients for the formation of heavier and heavier elements as the universe continued to expand. Gamow had formulated these ideas by 1940 and spent most of the 1940s working with physicists Ralph Asher Alpher and Robert Herman on mathematical calculations of heavy-element formation. Gamow presented the Big Bang theory publicly in 1948, and it was accepted by many astronomers as a valid interpretation of the astronomical evidence. In the decades since 1948, evidence to support parts of the theory has emerged, and it has for the most part been accepted as the best explanation for the origin of the universe.

Radio Astronomy

During the late 1930s and early 1940s Grote Reber made major advancements in radio astronomy. A young radio engineer at the Stewart-Warner Company in Chicago, Reber had read about Karl Jansky's 1931 discovery of naturally occurring radio waves coming from the sky. Reber planned how he could map the stars by measuring the distribution of the radiation intensity throughout the sky at different wavelengths. In 1937—in the yard of his Wheaton, Illinois, home—he built a radio telescope with a 9.5-meter parabolic reflecting dish that replaced the mirrors in a conventional telescope. Until 1947 he was the only active radio astronomer in the world. In November 1944 he published a complete sky survey, after collecting more than two hundred chart recordings. These radio maps revealed that the peak radiation intensity came from hot, bright stars at the center of our galaxy, located in the constellation Sagittarius. Reber also discovered that radio waves could penetrate the interstellar dust that obscures much of the Milky Way when it is viewed with conventional telescopes. His observations from 1945 to 1947 resulted in maps of the Milky Way with nearly three times better resolution of details than in previous charts. Reber's work led to wide-spread use of the radio telescope as an important astronomical tool, as scientists developed radio telescopes of increasing size and sophistication.

Galactic Astronomy

Walter Baade, working at the Mount Wilson and Mount Palomar Observatories in California, was able because of his access to these large telescopes to photograph stars in portions of remote galaxies—a technically difficult and theoretically important achievement that led to his division of stars into two stellar populations according to age. In population I are young stars, the most luminous of which are blue. Population II stars are older stars, the brightest of which are red. Population I stars are formed from the interstellar dust created by the explosion of population II stars and are particularly concentrated in areas of interstellar dust, as in the arms of spiral galaxies. Population II stars are located in dust-free regions, as at the centers of spiral galaxies, where star formation has long ago ceased. This classification of star populations represents a milestone in the history of stellar astronomy.

Sources:

George Gamow, The Creation of the Universe (New York: Viking, 1952);

John Gribbin, In Search of the Big Bang (New York: Bantam, 1986);

J. S. Hey, The Evolution of Radio Astronomy (New York: Science History Publications, 1973);

Albrecht Unsöld and Bodo Baschek, The New Cosmos, translated by William 3D. Brewer, fourth edition, revised (Berlin: Springer, 1991).