SECTION 5.—THE WORK OF THE TELESCOPE
Prevalent Misconceptions
The general idea of an astronomer’s work, as gathered from the questions and remarks of visitors, is that he sits at the eyepiece of the telescope sweeping the heavens in a search for new planets, comets or stars. The absolute futility of such a use of the telescope is evident when it is realized that the main field of the 72-inch covers only about one hundred-millionth of the sky and if only five seconds was required to examine each field it would take more than a lifetime to go over the whole sky once. A second misconception is the idea that large telescopes are used for visual observations of the planets with special reference to their habitability. No work is being attempted at this or other large observatories on planetary detail for which about an 18-inch refractor gives the best results and such a large telescope as the 72-inch is quite unsuited. All scientific observations with the 72-inch are made photographically and it is only arranged for visual use on Saturday evenings when for two hours visitors are allowed to observe the heavenly bodies. A third misconception is that the astronomer only works at night. However true this idea may have been in the days of visual observations when the measurements were made at the eyepiece, there is certainly now, when photography is so generally applied, more day than night work in astronomy. Besides the advantages of permanency, accuracy of measurement and power of recording objects beyond the range of the keenest eyesight, the photographic method has the further great advantage that an hour’s exposure may give sufficient material for several days’ measurement and discussion.
Spectroscopic Work
As already indicated most of the work with the 72-inch telescope is spectroscopic, but as also indicated modern spectroscopic investigations cover so wide a range of research that the actual work of the observatory is very varied. By aid of suitable spectrographs attached to a large telescope we can measure the speed of the stars towards or from us, their radial velocity as it is termed. We can discover double stars too close ever to be seen double in any telescope and we can determine the manner in which they revolve around one another and their distance apart and mass. From the spectra of the stars we can determine their absolute brightness as compared with the sun and their parallax or distance. The chemical elements present in the outer atmospheres of the stars can be determined and the pressure in these atmospheres. The measurement of temperatures and other physical conditions in the stars by means of the spectroscope is now an accomplished fact and one of the most recent developments of the spectroscopic work here has been to provide evidence of the truth of a theory of atomic structure and to show that the atomic constants in the enormous furnaces of the stars are the same as on the earth. Such a catalogue of information, obtained from an investigation of the mere quality of the light from stars so faint as to be quite invisible to the unaided eye and so distant that it may take thousands of years to travel to us, is sufficiently comprehensive to be treated in more detail.
Radial Velocities
When the 72-inch telescope was in course of design and construction, one of the greatest needs in astronomical work was increased data in regard to the radial velocities of the stars. Although the telescope was so designed as to be suitable for all kinds of observational work, special attention was devoted to the spectroscopic end. After consultation with the most prominent astronomers an observing programme of about 800 stars whose “proper” or cross motions across the sky were accurately known but whose radial velocities had not been determined, was prepared and spectroscopic observations of the stars on this programme were commenced as soon as the telescope was completed in May 1918. After slightly over three years’ work, observation and measurement were completed and Vol. II, No. 1 of the observatory publications, “The Radial Velocities of 594 Stars,” was published early in 1922. As hitherto the radial velocities of only about 2,000 stars had been obtained, this work was a considerable addition to existing data about the motions of the stars and will be of great use in extending our knowledge of the structure and motions of the universe. A second programme of 1,500 stars has been prepared but owing to other intervening observational work, not much has yet been done on this new programme.
One of the auxiliary programmes undertaken and nearly completed since the first programme is the determination of the radial velocities of a very interesting but limited class of stars, the highest temperature stars known, the O-type stars. The radial velocities and other interesting data about 50 of these stars have been completed.