Word: nebula
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Dates: during 1950-1959
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Astral Speedometer. The redshift was first discovered by Edwin P. Hubble, most famous of the Palomar astronomers, and on it he based his startling theory of "the expanding universe." The spectrum of an astronomical object (a star or nebula) shows numerous bright or dark lines, each representing light of a certain wave length. If the object is stationary in relation to the earth, the lines are in the same places as in the spectrum of the sun. But if it is moving away from the earth, the lines shift toward the red end of the spectrum, because the receding motion...
Blue to Green. The 200-inch Palomar telescope was built primarily for studying more distant nebulae. It can photograph them as faint blurs at distances something like one billion lightyears, but getting their spectra is more difficult. The light from the nebula is concentrated by the telescope's great mirror upon a prism, which spreads it into a spectrum one-tenth of an inch long. So dim is the image on the photographic plate that four to six hours of exposure are needed to make the picture...
...most distant nebulae studied so far, the bright "H" and "K" lines of glowing calcium, which are normally blue, are shifted into the green band of the spectrum. If they were bright enough to be seen in color, human eyes would actually see them as green instead of blue. This means that the motion of the nebula has lengthened the wave length of its blue light by more than 800 angstroms (.000003 in.). "It's a tremendous shift," says Dr. Hubble. "In our own stellar system, the average shift is only a fraction of one angstrom...
Extra-sensitive equipment was necessary, and the radio astronomers had to wait for still, rainless nights, though radio reception from the stars is not ordinarily affected by the weather. Six times they allowed the rotation of the earth to sweep the telescope past the nebula. Each time they moved the mast slightly to cover a different strip of sky. In the four middle sweeps they found what they were looking for: low peaks in the curves representing radio energy reaching the telescope. Careful analysis of the curves showed that the waves must have come from an oval object like...
...much radio energy is sent out by the Milky Way galaxy, another vast swirl of billions of stars, of which the sun is a part. Then they calculated what this radio source would look like to their radio telescope if it were as far away as the Andromeda nebula. The calculations showed that it would look much the same. This went far to prove what astronomers had long suspected: the Milky Way galaxy is a "twin...