ASTRONOMICAL NOTES

Press, Volume LXXI, Issue 21411, 1 March 1935, Page 4

ASTRONOMICAL NOTES

MARCH, 1935 (SPICULLT WRITTIV tOll THE PRESS.) [By E. O. HOOG, M.A., F.R.A.S.] The sun will enter the zodiacal sign Aries on March 22, when the equinox will occur. The planet Mercury will rise on March 1 at 4.28 a.m. and on March 15 at 4.4 a.m., and Venus will set on these dates at 8.12 p.m. and 7.50 p.m. respectively. Mars will rise on March 1 at 9.8 p.m. and on March 15 at 8.9 p.m., and Jupiter at 10.11 p.m. and 9.16 p.m. respectively. Saturn will not be visible during the early part of the month; it will rise on March 22 at 4.17 a.m. Mercury will on March 1 be about equal in brightness to a star of the first magnitude, and it will steadily increase in brilliance during the month. The apparent magnitude of Mars will increase from —0.4 to —l.l during March and its distance from the earth will diminish from about 73,850,000 miles to 59,130,000 miles. The apparent magnitude of Jupiter at the close of the month will be —1.9, when its distance from the earth will be about 431 million miles. There will be two interesting planetary conjunctions on March 22. At 7 p.m. on that day Venus and Uranus will appear to be separated by only 0.4 degrees, while two hours later the angular distance between Mercury and Saturn will be only 0.3 degrees. It will be necessary to use a small telescope or good field-glasses to see the earlier conjunction and, owing to the dimness of Uranus, Mercury and Saturn will have separated out a little by the time they become visible on the morning of March 23. The Golden Bees The two open clusters in the constellation Taurus—the Pleiades and the Hyades—have always been favourite objects with star gazers and many curious legends and associations cling to them. The Pleiades were said by Bayard Taylor in his Hymn to Taurus to "cluster like golden bees" about the bull's mane. It has been claimed that these stars were the first ever mentioned in astronomical literature, as they appear in the Chinese annals of 2357 8.C.; they show up in early Greek literature, Hipparchus and Aratus noticing seven, while Homer and Attalus could see but six. Greek mythology tells us that the stars were seven sisters who, with the exception of Merope, espoused gods, but she, having become enamoured of and married to the crafty Sisyphus, hid her face in shame when she reflected on her sisters' alliance with the Olympians. There is much evidence in support of the view that one of the Pleiades has declined in luminosity in historic times.

In the authorised version of the Bible we read in Job xxviii., 31, of the sweet influences of the Pleiades, and there is the marginal note 'Or, the seven stars.' Miles Coverdale, in the first complete English translation of the Bible, in 1535, A.D., has, opposite the same text, the marginal note. "Those VII. starres, the clock-henne" with her chickens, while in the Breeches Bible we have in the same context the following remark: "Which starres arise when the sun is in Taurus, which is the springtime, and brings flowers.",. Josephus, who makes very few stellar allusions, tells us that during the siege of Jerusalem by Antochus Epiphanes, in 170 8.C., the Jews suffered severely for want of water, but were relieved by "a large shower of rain, which fell at the setting of the Pleiades." Sometimes these stars have been called "flocks of birds," sometimes "maidens dancing," sometimes "hen and chickens." The .Little Sows The V or wedge-shaped group of stars lying round the red giant, Aldebaran, is known as the Hyades; its members are so scattered as to form a more open cluster than do those of the Pleiades and one of far less interest to the observer. It is said that their familiar title among the Roman country folk was Suculas—the little pigs or little sows—a name which Pliny explains as due to the fact that "the continual rains at the season of their setting made the roads so miry that these stars seem to delight in dirt, like swine." Among the Arabs they appear to have been known as the little she camels, in distinction to Aldebaran, the large camel, and the story is that Aldebaran drove them before him as evidence of his wealth when he went to woo the Pleiades, who had previously spurned his advances on account of his poverty. In the Greek mythology the Hyades were regarded as the daughters . of Atlas and /*Ethra, and consequently as half-sisters of the Pleiades, whose father was also Atlas. Both groups together formed the nurses or governesses called the Atlantides, to whom

was entrusted the bringing up of Bacchus. They were always thought to indicate wet weather, hence possibly the origin of their name, although it was also held that their habit of weeping for the loss of their only brother, Hyas, was the cause of the downpour they made. This association of the group with unpropitious weather is preserved for us by Tennyson in tho lines:— Thro' scudding drifts the rainy Hyades Vext the dim sea. The Ozone Layers In these notes for May last attention was drawn to the part played by the ozone layers of the atmosphere in restricting observation of the solar and stellar spectra; they block out entirely radiation of certain wave-lengths, lying for the most part in the ultra-violet region of the spectrum. These wavelengths are measured in Angstroms, the Angstrom being one-millionth part of a centimetre, and the wave-lengths of the radition which we perceive as light extend from 7600 A to 3900 A, when the ultra-violet spectrum begins. fStellar radiation longer than 2950 A can pass through the ozone layers! but waves shorter than the figurefflast mentioned are almost completely absorbed and it seemed as though no further progress in our knowledge of the radiation coming to us from an external source could be made. It is therefore most interesting to know that three Swiss scientists, Meyer, Schein, and Stoll, have succeeded in detecting and measuring solar radiation whose wave-length lies between 2400 A and 2000 A, thus opening out a new field of investigation for solar physicists. Our increased knowledge during recent years of the intrared and ultra-violet parts of the solar and stellar spectra has been due to the use of aluminised mirrors and improvements in photographic methods and plates but this latest achievement has been made by quite other means. For many decades after the death of Newton the corpuscular theory of light which he had propounded was generally accepted as the true explanation of optical phenomena; gradually, however, observations accumulated which could not be accounted for satisfactorily on this theory and it was displaced by the undulatory theory which supposed radiation to be transmitted by a species of wave motion in an ether pervading all space. Until recent days no physical theory was supposed to stand on a more secure basis than the undulatory theory of light, but modern research has revealed a large number of phenomena for which the accepted theory could not afford a satisfactory explanation and the labours of Planck, Einstein, and others have shown that the undulatory theory must be supplemented by the quantum theory, under which a beam of light is regarded as composed of discrete units, called "light-quanta" or "photons," just as a shower of rain is broken up into separate drops of water. The reconciliation of the undulatory and quantum theories or their relation to each other is one of the most pressing problems confronting the physicist of to-day. The Swiss scientists have attacked the radiation problem in its quantum and not in its undulatory aspect. They took with them to the high altitude of the Jungfraujoch in Switzerland not a camera but a "photon" counter, a delicate instrument winch registers the number of photons which fall on a given area in a given time and have demonstrated that there is a gap in the spectrum through which radiant energy can pass, though it is blocked on either side by the ozone layer. This method of approach is in its infancy*, and it is impossible as yet to say what secrets of nature its further application may reveal, but Dr. Shapley, to whom we are indebted for a brief note on the subject, evidently regards the discovery as one of the most valuable made in recent days.

The Height of the Ozone Layer Professor Regener, of the Physical Institute, Stuttgart, has been exploring the stratophere to heights between VI and 20 miles above the earth's surface by means of small free-flight balloons, which carry aloft automatic instruments. Some bearing a quartzspectrograph rose to altitudes of 12.5, 13 and 19.5 miles. An examination of sunlight at these heights disclosed that at 13 miles 40 per cent.' of the ozone layer was then below the instrument, while at 19.5 miles 70 per cent, of it was below the instrument. These results confirm recent calculations which predicted that the height of the ozone layer is much less than was previously supposed. Its Protective Power The ozone layer absorbs very strongly the ultra-violet rays of sunlight; without its pressure sunlight and heat would be so intense that animal life as we know it could not exist. In a recent broadcast talk, Sir James Jeans told his hearers: "If the colour filter of ozone were suddenly removed, the physicists' instruments would disclose the fact at once. So would the skins of our bodies. We should become browner and browner until we became at last quite black — burnt up by the new light—at least if we survived so long, for I do not think we should live for long if all the rays of the sun fell upon us. Thus

this layer of ozone fulfils the important function of keeping us alive. If we could equip ourselves with eyes to see all colours and could momentarily pass beyond the ozone layer, we should see a wonderful sight. The stars would appear incomparably brighter and more vivid then they do now, with the ozone layer cutting otf the greater part of their radiation and their colours would be far more vivid." Sir James went on to say that were there no layer of ozone to cut off the ultra-violet light it was quite likely that our atmosphere would conduct electricity much as a sheet of metal did We should hardly be able to use electricity in any form since our atmosphere would conduct it away as quickly as it was generated, and our wireless sets would be useless.