In modern applications, a redshift of light represented by z is defined by The Doppler effect has several important manifestations, all connected with changes in wave behavior when the source and the observer of the waves move with respect to each other. Slipher interpreted these wavelength shifts by referring to an effect first described in 1842 by Johann Doppler. The terms “red” and “blue” do not denote actual colors, only the direction of the shift to longer or shorter wavelengths. Most of the galaxies Slipher observed exhibited “redshifts,” however, toward longer wavelengths. When he observed the M31 galaxy, for example, the shift was toward short wavelengths, a “blueshift” because blue is on the short-wavelength end of the visible spectrum. He discovered that characteristic spectral lines in light received from galaxies were slightly shifted in wavelength from what is observed for the same lines in an earthly laboratory. Slipher worked with a large refracting telescope equipped with a spectroscope, a device that analyzes light by spreading it into its rainbow components. His greatest achievement, probably the most important by an astronomer in the twentieth century, was inspired by a series of observations made in the 1910s by a largely self-taught astronomer named Vesto Slipher at the Lowell Observatory in Flagstaff, Arizona. He was patient.” We have seen Hubble's masterful use of the Leavitt- Shapley method for measuring cosmic distances. In one of his rare compliments for Hubble, Shapley said (more than a decade after Hubble's death), “Hubble, by the way, was an excellent observer, better than I. One aspect of Hubble's genius was his ability to take the incomplete work of others and carry it further with his own extensive and carefully planned observations.
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