1939: Astronomy

New Equipment.

One of the outstanding events of the year in the astronomical field was the dedication, May 5-8, of the W. J. McDonald Observatory. Located on Mount Locke, near Fort Davis, Texas, it is to be operated cooperatively by the Universities of Texas and Chicago. In the words of its president-elect, Dr. Homer P. Rainey, 'the University of Texas had the funds for an observatory but did not possess a faculty in astronomy . . . while the University of Chicago had an outstanding faculty, but was in need of more and better equipment for observation.' The dedication was made the occasion of a symposium in which leading experts in this country and abroad were invited to take part. The field under discussion was that of the galactic and extra-galactic structure in relation to the universe as a whole.

The main instrument, an 82-inch reflector, second in size only to the 100-inch reflector of the Mt. Wilson Observatory (and third to the Mt. Palomar 200-inch reflector), has been designed, according to Director Otto Struve, to be as efficient as possible for the study of the spectra and brightness of individual stars and nebulae. The telescope is made very short (f/4) and hence will gain in power by the smallness of the star images. A special spectrograph converts it into an f/2 instrument. In Director Struve's words: 'There are a billion stars or more which have never even been looked at and which this telescope will be capable of analyzing and classifying.'

The telescope was in full operation for several weeks before the dedication. Kuiper had already taken separate spectrograms of 300 stars which he knew to be relatively near because of their large proper motion. Two of them turned out to be of the type he was hoping to identify — 'white dwarfs.' This discovery raises the known number of these enormously dense stars of stripped atoms to 18.

The favorable latitude of the new observatory, making accessible regions of the sky which cannot be successfully reached from the more northern observatories, coupled with the large amount of clear weather, the good vision, and the enthusiasm of the staff should bring rich results.

The Buhl Planetarium in Pittsburgh is the fifth to be installed in the United States. The building contains a public observatory, lecture room and exhibit hall. A special feature is the room for amateur telescope makers. James Stokley, formerly at the Fels Planetarium in Philadelphia, is the director.

A Schmidt camera with the speed of an f/9.62 ratio has been constructed at the Mt. Wilson Observatory without excessive steepness of the curves of the correcting plate. The mirror is solid and silvered on the back. The photographic plate, one-half inch square, is pressed against the upper surface of the mirror at a distance from the reflecting surface of one-half the radius of curvature. (Christic and Hendrix contributed a very instructive article on the Schmidt camera to the August 1939 number of the Scientific American.)

Experiments in Solar Radiation.

With the gift of Godfrey L. Cabot 'for research on the utilization of solar radiation for the tasks of man,' experimentation is well under way at the Massachusetts Institute of Technology on efficient ways of trapping the heat of the sun on the roof of a house and storing it in the basement. An experimental house has been built which will be heated in winter and air conditioned during the summer with solar energy. Water, heated in tubes on the roof, will be piped to a large well-insulated water storage tank in the basement where it is expected to keep the water hot for several months, thus smoothing over the cloudy and sunny weather.

A 'solar-silo,' to collect and store heat from a solar heater, has been suggested by F. G. Cottrell. It would consist of a deep, cylindrical, concrete-lined pit, filled to near the top with loose, dry sand and closed with about ten feet of glass wool. Heated air would be brought to the top of the sand and drawn off as needed from the bottom.

Photography As an Aid to Astronomy.

A complete ring of light around the dark disk of Venus when it is nearly between us and the sun, which had previously been observed visually, was successfully photographed at the Lowell Observatory. Its brightness suggests that there are fine dust particles scattered through the gaseous atmosphere.

In order to take full advantage of the unusually close approach of Mars in 1939, by going where it would reach a high altitude, E. C. Slipher, who has been photographing Mars in different colors at every opposition, took his cameras and plates to Bloomfontein, Orange Free State.

At the Lick Observatory Wright has made a careful observational study by the spectroscopic method of the rotation period of Saturn. He finds at the equator a period of 10 hours and 2 minutes, which is about 2 per cent shorter than that found from the few observations of spots. He confirms the hitherto scanty evidence of an increase in period up to latitude 36° and shows that there is a further increase in higher latitudes.

McMath and Sawyer have given a summary (Publ. Observatory Michigan, vol. 7, No. 9) of their motion picture work on solar prominences with the tower telescope at Lake Angelus. A nearly continuous watch is kept for eruptions on the sun and as soon as the beginnings of a prominence are sighted operation of the complicated and ingenious photographing mechanism, even to photo-electric 'guiding,' is started and continued as long as the prominence performs. 'Frames' are secured at the rate of four or more per minute. In the three years that the tower telescope has been in operation, over 150,000 exposures have been made. Improvement in the speed and precision of projection and measurement of the films has also been carried forward, so that the ease and accuracy of the study of this great wealth of material is now comparable with that attained in the taking of the pictures.

The pictures, showing the astonishing development of a prominence and giving an almost continuous record of the motion of knots and streamers furnish a rapidly accumulating store of material of great scientific value.

The authors present arguments for believing that the apparent motion in prominences is really a motion of material rather than a travelling excitation. They also outline a new classification of prominences and summarize the conclusions they have drawn from their observations.

The 'coronaviser,' devised by A. M. Skellett, is another promising instrument for observing solar prominences and corona without an eclipse. It is a special television apparatus which scans the sky around the sun, separating the component of the photo-electric current arising from the glare (mainly a d-c component) from that arising from the coronal features (mainly a-c) and amplifying the latter component. The reproduction appears on the screen of a cathode ray tube. Numerous images of prominences have been obtained and a number of the images showed features that apparently were of coronal origin. (See also PHOTOGRAPHY.)

Comets.

This was a very rich year for comet seekers. No less than twelve comets were found. One more discovery was announced, but several observers with large telescopes looked in vain for it and so it was regarded as unverified and was not given a designation. Of the twelve, seven were known periodic comets returning to the neighborhood of the sun and were detected by professional astronomers with large telescopes close to their calculated positions. The other five were new comets discovered in systematic search with small telescopes. Comet 1939d was the brightest in several years. On April 19 it was of the third magnitude. Brightness, however, goes with nearness to the sun, and it was necessary to look at just the right time after sunset and have a northwest horizon that was free of trees, buildings, and clouds. It was the most discovered comet of the year. Hassel first reported it from Oslo, but it was soon learned that two Russian astronomers had discovered it just ahead of him. So it has been labeled the Jurlof-Achmarof-Hassel comet. Reports of other independent discoveries kept coming in for several days but no further additions were made to the comet's name. The new comet 1939b has now been observed long enough to show that it is moving in an elliptic orbit so it is expected that this comet, to be known after the discoverer as Comet Vaisala, will be back in about ten years. Comet Rigollet, another of the new ones, is found by Cunningham to have practically the same orbital elements as a comet discovered in 1788 by Caroline Herschel and apparently never seen since.

Watchers were all ready on the nights of October 9 and 10 for a repetition of the brief but brilliant meteoric shower which had occurred six years ago. The earth was again crossing the orbit of the Giacobini-Zinner comet and, while the comet itself was not yet at the rendezvous, it was anticipated that enough debris left behind by the comet might have become scattered along its path to give a display. No reports of any sizable shower have been made. Chances may be better next year when the earth crosses the orbit behind the comet.

Sun's Energy.

Bethe's picture (Physical Review, 55, 434) of the maintenance of the sun's output of energy, for which he received the A. Cressy Morrison prize, is essentially the consumption of hydrogen with the production of carbon and helium and the release of energy. The complicated atomic reaction which he finds would produce the observed output of energy may interest some readers. The first step is the combination of hydrogen and carbon producing an isotope of nitrogen of atomic weight 13. Being unstable this breaks down into an isotope of carbon of the same atomic weight and releases a positive charge of electricity. Another hydrogen nucleus combines with the carbon 13 producing nitrogen. This unites with a third hydrogen nucleus and an isotope of oxygen of atomic weight 15 is formed. This breaks down into nitrogen 15 and releases another charge of electricity. The nitrogen takes on another hydrogen nucleus and breaks up into carbon and a helium nucleus. Following out this theory one concludes that in the 'white dwarfs,' like the companion of Sirius, hydrogen has been practically all used up.

The Milky Way.

Stebbins and his associates have made a big contribution toward the true picture of our galaxy by their measurement, with the photo-electric photometer, of the color excesses of 1332 of the bluer stars. They have determined with much increased accuracy how much yellower some of these stars are than they should be according to their spectral type. Those most affected are in or near the plane of the Milky Way, but the effect is larger in some patches than in others. This leads to a determination of the total absorption of starlight as it comes through different regions and different distances. There is much corroborative evidence of this obscuring matter. Color excess is one of the most potent means for outlining its extent and hence making allowance for its effect on the apparent brightness of stars. The brightest patches of the Milky Way are only half as bright as they would be if there were no obscuring matter. In some areas only as little as 1/20 to 1/40 of a star's light gets through a distance of one thousand parsecs. One can realize how badly deceived astronomers were in judging distance by apparent brightness before they knew that a lot of the dimming was produced by obscuring matter and not by distance.

Schilt thinks he has evidence from his statistical studies that the measured parallaxes of stars are considerably too large and hence the accepted distances of the nearer stars too small, owing to systematic errors in the measurements.

Shapely announces that our galaxy is surrounded by faint stars of very high velocities of recession which unquestionably belong to our galaxy but are now far beyond the accepted limits of the galaxy. He points to similar star-halos around other galaxies, such as the Andromeda nebula.

Supernovae.

Three more 'supernovae' have been discovered by Zwicky with the 18-inch Schmidt telescope on Mt. Palomar. Another one was found at Harvard on a plate taken in 1937. Zwicky's discoveries in his systematic search since the Schmidt telescope was put in operation number just about one-half those reported in all astronomical history. He still thinks his earlier estimate of the frequency of appearance of supernovae as about one per nebula per 600 years is about right. The great number of the spiral nebulae, in which they appear, is the thing that makes the systematic watch worth while.

Honors Awarded.

Among this year's honors is the award of the Bruce Gold Medal of the Astronomical Society of the Pacific to Harlow Shapley. A letter is sent each year to the directors of six observatories (named in the deed of gift) asking each to nominate not more than three persons 'for distinguished services to astronomy.' The directors of the society then select the medalist from those nominated.

Several astronomers from America attended a congress on astrophysics held in Paris, July 17-23, under the chairmanship of H. N. Russell. Novae, white dwarfs, and the life history of a star were especially considered.

Necrology.

Sir Frank Dyson, Astronomer Royal of Scotland from 1905 to 1910, and Astronomer Royal of England from 1910 to 1933, died on May 25 while on a voyage from Australia to South Africa. He was 71 years old.

Suggested Reading.

In May 1937 the International Council of Scientific Unions established The Committee on Science and its Social Relations 'to promote thought upon the development of the scientific world picture and upon the social significance of the applications of science.' The report on astronomy, prepared by Bart J. Bok is printed in Popular Astronomy 47, 356. Among its topics it includes the popularization of astronomy (books and periodicals, planetaria and museums, adult education and public nights at the observatory, the press and the radio); the activities of the amateur astronomical societies of the world and the lines of research that are open to amateurs; where to find abstracts of papers and reports of research in progress; and what has been accomplished by international cooperation. It is an extremely valuable contribution.

Those interested in the many pioneering problems met with and solved in the construction of the world's greatest telescope on Mt. Palomar will be entertained with David O. Woodbury's book The Glass Giant of Palomar. Dr. Adams gives a very readable account of the optical figuring of the 200-inch mirror, the design and construction of the mounting and the work done on Mt. Palomar to make it habitable in Nature, Feb. 25, 1939, and reprinted in Journal Royal Astronomical Society Canada, July. Aug. 1939.

Astronomy, by W. T. Skilling and E. S. Richardson, New York, Henry Holt and Co., 1939, pp. 579, $3,00, is described by one reviewer as '. . . not too difficult for a student with very little scientific background, yet fairly complete and up to date in its treatment of the latest advances in the subject.'