ILLUSTRATIONS

FIG.

  1. [The Constellation of Orion (Hubble)]
  2. [The Great Nebula in Orion (Pease)]
  3. [Model by Ellerman of summit of Mount Wilson, showing the observatory buildings among the trees and bushes]
  4. [The 100-inch Hooker telescope]
  5. [Erecting the polar axis of the 100-inch telescope]
  6. [Lowest section of tube of 100-inch telescope, ready to leave Pasadena for Mount Wilson]
  7. [Section of a steel girder for dome covering the 100-inch telescope, on its way up Mount Wilson]
  8. [Erecting the steel building and revolving dome that cover the Hooker telescope]
  9. [Building and revolving dome, 100 feet in diameter, covering the 100-inch Hooker telescope]
  10. [One-hundred-inch mirror, just silvered, rising out of the silvering-room in pier before attachment to lower end of telescope tube. (Seen above)]
  11. [The driving-clock and worm-gear that cause the 100-inch Hooker telescope to follow the stars]
  12. [Large irregular nebula and star cluster in Sagittarius (Duncan)]
  13. [Faint spiral nebula in the constellation of the Hunting Dogs (Pease)]
  14. [Spiral nebula in Andromeda, seen edge on (Ritchey)]
  15. [Photograph of the moon made on September 15, 1919, with the 100-inch Hooker telescope (Pease)]
  16. [Photograph of the moon made on September 15, 1919, with the 100-inch Hooker telescope (Pease)]
  17. [Hubble's Variable Nebula. One of the few nebulæ known to vary in brightness and form]
  18. [Ring Nebula in Lyra, photographed with the 60-inch (Ritchey) and 100-inch (Duncan) telescopes]
  19. [Gaseous prominence at the sun's limb, 140,000 miles high (Ellerman)]
  20. [The sun, 865,000 miles in diameter, from a direct photograph showing many sun-spots (Whitney)]
  21. [Great sun-spot group, August 8, 1917 (Whitney)]
  22. [Photograph of the hydrogen atmosphere of the sun (Ellerman)]
  23. [Diagram showing outline of the 100-inch Hooker telescope, and path of the two pencils of light from a star when under observation with the 20-foot Michelson interferometer]
  24. [Twenty-foot Michelson interferometer for measuring star diameters, attached to upper end of the skeleton tube of the 100-inch Hooker telescope]
  25. [The giant Betelgeuse (within the circle), familiar as the conspicuous red star in the right shoulder of Orion (Hubble)]
  26. [Arcturus (within the white circle), known to the Arabs as the "Lance Bearer," and to the Chinese as the "Great Horn" or the "Palace of the Emperors" (Hubble)]
  27. [The giant star Antares (within the white circle), notable for its red color in the constellation Scorpio, and named by the Greeks "A Rival of Mars" (Hubble)]
  28. [Diameters of the Sun, Arcturus, Betelgeuse, and Antares compared with the orbit of Mars]
  29. [Aldebaran, the "leader" (of the Pleiades), was also known to the Arabs as "The Eye of the Bull," "The Heart of the Bull," and "The Great Camel" (Hubble)]
  30. [Solar prominences, photographed with the spectroheliograph without an eclipse (Ellerman)]
  31. [The 150-foot tower telescope of the Mount Wilson Observatory]
  32. [Pasadena Laboratory of the Mount Wilson Observatory]
  33. [Sun-spot vortex in the upper hydrogen atmosphere (Benioff)]
  34. [Splitting of spectrum lines by a magnetic field (Bacock)]
  35. [Electric furnace in the Pasadena Laboratory of the Mount Wilson Observatory]
  36. [Titanium oxide in red stars]
  37. [Titanium oxide in sun-spots]
  38. [The Cavendish experiment]
  39. [The Trifid Nebula in Sagittarius (Ritchey)]
  40. [Spiral nebula in Ursa Major (Ritchey)]
  41. [Mount San Antonio as seen from Mount Wilson]

[CHAPTER I]

THE NEW HEAVENS

Go out under the open sky, on a clear and moon-less night, and try to count the stars. If your station lies well beyond the glare of cities, which is often strong enough to conceal all but the brighter objects, you will find the task a difficult one. Ranging through the six magnitudes of the Greek astronomers, from the brilliant Sirius to the faintest perceptible points of light, the stars are scattered in great profusion over the celestial vault. Their number seems limitless, yet actual count will show that the eye has been deceived. In a survey of the entire heavens, from pole to pole, it would not be possible to detect more than from six to seven thousand stars with the naked eye. From a single viewpoint, even with the keenest vision, only two or three thousand can be seen. So many of these are at the limit of visibility that Ptolemy's "Almagest," a catalogue of all the stars whose places were measured with the simple instruments of the Greek astronomers, contains only 1,022 stars.

Back of Ptolemy, through the speculations of the Greek philosophers, the mysteries of the Egyptian sun-god, and the observations of the ancient Chaldeans, the rich and varied traditions of astronomy stretch far away into a shadowy past. All peoples, in the first stirrings of their intellectual youth, drawn by the nightly splendor of the skies and the ceaseless motions of the planets, have set up some system of the heavens, in which the sense of wonder and the desire for knowledge were no less concerned than the practical necessities of life. The measurement of time and the needs of navigation have always stimulated astronomical research, but the intellectual demand has been keen from the first. Hipparchus and the Greek astronomers of the Alexandrian school, shaking off the vagaries of magic and divination, placed astronomy on a scientific basis, though the reaction of the Middle Ages caused even such a great astronomer as Tycho Brahe himself to revert for a time to the practice of astrology.