In the measurement of the radial velocity of the 800 stars on the first programme it was found that in about 180 stars successive plates did not give constant velocities, the stars at one time approaching at another receding from us. This phenomenon is practically certain proof that we are measuring the velocity of a star revolving around an invisible companion and such stars are generally called spectroscopic binaries to distinguish them from visual binaries which can be seen double in the telescope. Over 200 spectroscopic binaries have been discovered at this observatory as compared with about 700 discovered elsewhere, again a considerable addition. In about 20 of these binaries, observations were continued until the period of revolution, the form of the orbit, the separation of the two stars and in some cases, their masses were determined. In a particular class of spectroscopic binaries, the eclipsing variables, which allow from the combination of spectroscopic and photometric measurements the absolute dimensions to be obtained, we were able to determine the separation of the two stars, their diameters, densities, masses and brightnesses and the probable distances. Such complete information has been obtained here about seven systems, while only seven other systems have been determined elsewhere.
Absolute Magnitude and Distance
A new application of spectroscopic methods is to the determination of the total brightness of the stars as compared with the sun and their distance or “spectroscopic parallax” as it is called. This depends not on the positions but on the relative intensity or strength of the lines in the spectra of the stars and has only been developed in the last three or four years. The absolute magnitude and spectroscopic parallax of about 800 stars is now nearly completed and will soon be published while as a side line the radial velocities of 125 more stars have been determined.
Physical Conditions in the Stars
The spectrographs have also been used by one member of the staff in the determination of the physical and chemical conditions in stellar atmospheres, a new and difficult problem but one which promises not only very valuable additions to our knowledge of the constitution of the stars but may also lead to economic applications of the greatest importance. A new method depending upon the use of a wedge of dark glass has been applied to determining the distribution of energy in the different parts of the spectrum of the stars and to measuring their temperatures, while an application of the same methods to individual lines may lead to a great increase in our knowledge of conditions in the stars. A special investigation of three of the high temperature O-type stars referred to above has proved the existence in the spectra of these stars of lines predicted as present from purely theoretical conditions but never previously identified and has thus remarkably verified a theory of the structure of the atom. The measurement of the wave lengths of these hitherto unknown lines has led to an important independent determination of the fundamental constants of atomic structure and the dimensions of the atom and has shown that these constants and dimensions are the same in the tremendous furnaces of the stars as in our terrestrial laboratories, a verification of the homogeneity of matter and the uniformity of physical laws throughout the universe. Further interesting results from this investigation are the application of a new theory of ionization with the probable relative abundance of the elements to an independent determination of the temperature of these stars.
Other Investigations
Direct photographs have been made of some nebulae and clusters but this work is not being definitely followed at present. Investigations into the phenomena accompanying some short period binaries have been made and into the behaviour of the two strong calcium lines H and K in the spectra of the high temperature stars from which interesting and valuable results are expected. Since the observatory commenced work two bright novae or new stars have appeared, which have been fully observed spectroscopically here and the results discussed. The plates of the nova in Aquila have been loaned to the observatory at the University of Cambridge, England, for fuller discussion and analysis.
Value of Astronomical Work
This brief sketch of the work of the observatory naturally leads to the question frequently asked of astronomers:—What use is the work done at observatories and what practical value can a knowledge of the stars have in everyday life? While astronomy has obvious practical applications to navigation and surveying yet nine-tenths of modern astronomical research is devoted to the more or less abstract question of the constitution and motion of the stars and the structure of the universe. Indeed most physical and chemical as well as astronomical research is undertaken for the purpose of increasing our knowledge and of investigating the secrets and laws of nature and has generally no direct practical economic application. But it is now generally recognized by the layman as well as the scientist that without abstract there can be no applied science and that all the great economic and industrial applications of science have had to be preceded by the abstract and apparently non-practical investigations of pure science. The Great War perhaps made more evident than ever before the absolute dependence of applied science upon the unselfish and abstract work of pure science.