red shift or redshift, in astronomy, the systematic displacement of individual lines in the spectrum of a celestial object toward the red, or longer wavelength, end of the visible spectrum. The effect was discovered by V. M. Slipher of Lowell Observatory. Some red shifts are the result of the Doppler effect , i.e., of the relative motion of the earth and the object away from each other. The amount of displacement is a function of the object's recessional velocity relative to the observer. All distant galaxies show a red shift proportional to their distance from the earth as a result of the general expansion of space-time (see Hubble's law ). Known as the cosmological red shift, this results when the wavelength of light is stretched as it moves through the expanding universe. Red shifts are also produced by gravitation (the gravitational red shift) in accordance with the general theory of relativity . Because of the strong gravitational field, the frequency of the light emitted by atoms in a dense, compact star will be lower and the wavelengths consequently longer; such effects have been observed in white dwarfs . Not all celestial bodies have spectra displaced toward the red end of the spectrum. Of the billions of known galaxies, about 100—for example, the Andromeda Galaxy —are blue-shifted, indicating that they are approaching earth rather than receding from it. Most of these are dwarf galaxies in Milky Way's Local Group and in orbit about one another. See also blue shift ; cosmology .

red shift (z) Lengthening of the wavelength of light or other electromagnetic radiation from a source, caused either by the source moving away (the Doppler effect) or by the expansion of the universe (cosmological red shifts). It is defined as the change in the wavelength of a particular spectral line, divided by the rest wavelength of that line. The Doppler effect results from motion through space; cosmological red shifts are caused by the expansion of space itself stretching the wavelengths of light travelling towards Earth.

THE RED SHIFT: DISCOVERING AN EXPANDING UNIVERSE

Clouds in the Heavens

In the early 1920s Vesto M. Slipher, an astronomer working at the Lowell Observatory near Flagstaff, Arizona, was examining spiral-shaped nebulae in the night sky. According to contemporary scientific opinion these nebulae were cloudy patches of light caused by gases, but Slipher came to the conclusion that they were entire, separate galaxies like the Milky Way.

BIRD PSYCHOLOGIST

Among the most significant ornithological studies of the 1920s was the work of a child psychologist, Margaret Morse Nice (1883-1974), who had a master's degree in psychology and wrote articles on that subject at the same time she was studying birds. Nice's consuming interest was the observation of behavior, whether in her five daughters (the "research subjects" of her writings on psychology) or birds.

By 1920 Nice had decided she preferred bird-watching to people-watching and published the first of thirty-five articles that led to The Birds of Oklahoma (1924), the first complete study of that subject, which she wrote with her husband, Leonard Blaine Nice, head of the physiology department at the University of Oklahoma.

Margaret Nice's early bird studies are largely descriptive, but by the mid 1920s she had begun careful observations of their behavior, inspired by watching captive wild birds that she kept as pets. (Guests often found themselves sharing the dinner table with sparrows.) After the Nices moved to Ohio in 1927, she began her most important work, her studies of the behavior of song sparrows. She kept track of individual birds in the wild by placing colored bands on their legs and giving each one a name and a number. Never before had anyone followed a species of birds so closely, and when the final compilation of her research was published in two volumes as Studies in the Life History of the Song Sparrow in 1937 and 1943, it established her reputation as one of the foremost ornithologists in the world.

Source:

Christopher Cornog, Eetry on Mtrgaret Nice, in Notable American Women: The Modern Period, A Biographical Dictionary, edited by Barbara Sicheriman and Carol Kurd Green, with llene Kantrov and Harrette Walker (Cambridge, Mass,: Harvard University Prese, 1980).

The Doppler Effect

By 1923 he had measured the Doppler shifts of some forty-one of these star clusters. Discovered by Austrian scientist Christian Doppler, the Doppler effect describes the changes in sound or light waves transmitted from one body to another as they get closer together or farther apart. As objects move closer, waves get shorter and their frequency gets higher, and as light-wave frequencies get higher their color shifts toward the blue range. An object moving away emits longer waves with a lower frequency, and thus light waves in this category exhibit a red shift. Slipher detected red shifts in thirty-six of the galaxies he examined, meaning that they were moving away from Earth. The remaining five nebulae exhibited a blue shift, which seemed to mean that they were getting closer to Earth, but in 1925 it was discovered that the Milky Way is itself rotating rapidly. Failure to account for this spin had led to false blue-shift readings. After correcting for this factor, it was found that only two galaxies, both comparatively near to our own, showed a net blue shift. Slipher's work supported the research Edwin Hubble was doing at the same time on the expanding universe.

Source:

Isaac Asimov, Asimov's New Guide to Science (New York: Basic Books, 1984).