Page:Popular Science Monthly Volume 86.djvu/218

214  7. The Mount Hamilton and Santiago spectographicspectrographic [sic] observations of stellar motions have shown that stars effectively young are traveling slowly, middle aged stars more rapidly, and old stars more rapidly still; that is, that the velocities of the stars increase with their effective ages. 8. Observations have established that those nebulæ known as planetary nebulæ are traveling through space with average speeds even higher than the average speeds of the stars. It had previously been supposed that these nebulæ represented a stage of existence antecedent to the stellar age. The high velocities of these objects have created the opinion that they have more probably been formed from stars which have been overtaken by catastrophes, such as collisions with other celestial objects. 9. The North Pole Star was found to be a triple star, in 1899, by means of spectrographic observations. The first magnitude star Capella was discovered to consist of two stars revolving around their center of mass in 104.1 days, the two nearly equal components being inseparable in our largest telescopes. 10. In the same manner about 250 spectroscopic binary stars have been found at Mount Hamilton and Santiago. 11. A study of the orbits of spectroscopic binary stars has established that the component stars in a system whose spectrum indicates early age are relatively very close together, requiring very short periods of revolution, and that the orbits are nearly circular. In systems whose spectra show them to be of greater effective ages, the distances separating the components are successively greater, on the average, and their orbits are more eccentric. The observed facts on the subject are fully confirmative of existing mathematical theories of the evolution of double star systems. 12. The Crossley reflecting telescope established for the first time the tremendous advantage of this form of telescope in the photography of certain classes of celestial objects, such as nebulæ, star clusters, etc. 13. Before the Crossley reflector was in use about 10,000 nebulæ had been discovered at various observatories. A few dozens of these were known to be spiral in form. The Crossley photographs led to the discovery of many hundreds of additional nebulæ in the extremely small part of the sky covered by the photographs. It was a simple matter to calculate that certainly 120,000 and possibly half a million nebulæ await discovery whenever time can be spared for the Crossley reflector to undertake this work. These photographs led to the unexpected discovery that a majority of the nebulæ are of spiral form—undoubted evidence of their rotation. 14. The extensive series of photographs of the minor planet Eros and surrounding stars, with the Crossley reflector, led to a new and accurate determination of the distance from the earth to the sun. 15. Eight total solar eclipses have been successfully observed by expeditions whose expenses were defrayed by friends of the observatory. 16. It has been shown that the new stars appearing in recent years have been converted into nebulæ, and later, in many cases, into extremely faint stars of apparently normal condition. 17. Many thousands of extremely accurate positions of the stars have been secured with the meridian circle. 18. Very extensive observations of double stars, comets, planets, and satellites have been made. 19. A large number of orbits have been computed for visual double stars, spectroscopic binary stars, comets, and asteroids. 20. Extensive additions have been made to our knowledge of the spectra of nebulæ, comets, new stars, and stars of special interest.