Seth B. Nicholson

FRANK ELMORE ROSS, 1874-1960

Frank Ross was born in San Francisco on April 2, 1874, and received his early education in the schools of that city. He graduated from the University of California with a B.S. degree in 1896. After graduation, he taught mathematics and physics for one year in the Mount Tamalpais Military Academy and then returned to the University of California for graduate work. In his first year as a graduate student he had a fellowship at Berkeley and in his second year was a fellow at the Lick Observatory. Before receiving his Ph.D. degree from the University of California in 1901, he spent one year at the University of Nevada where he was an assistant professor of mathematics. After graduation Dr. Ross computed perturbations of the Watson Asteroids for one year and then went to Washington, D.C., where for a year he was an assistant in the Nautical Almanac Office and for two years served as a Research Assistant of the Carnegie Institution of Washington. In that capacity he worked under Simon Newcomb on planetary and lunar problems and, at Newcombs suggestion, computed a definitive orbit of Phoebe, the ninth satellite of Saturn. This orbit, which was published in the Annals of the Harvard College Observatory in 1905, was his first major independent publication in astronomy. In 1904, Dr. Ross married Margaret Benton and in 1905 they went to Gaithersburg, Maryland, where Dr. Ross became director of the International Latitude Observatory. There he completed the computations of the orbits of the sixth and seventh satellites of Jupiter that he had begun in Washington, and published them in the Lick Observatory Bulletin and the Astronomische Nachrichten, respectively. For the next ten years Dr. Ross continued

SUNSPOT ACTIVITY DURING 1947

During 1947 sunspots were more numerous than during any other year of the past century. The mean relative sunspot number for May 1947 was 206.5, the second largest for any month since 1749, which was the first year for which monthly relative sunspot numbers have been assigned. The only larger number was 238.9, for May 1778. In December 1836 the mean number was 206.2, essentially the same as that for last May. Only two other months, January 1837 and October 1847, have had relative sunspot numbers larger than 180. The sun was observed at Mount Wilson on 337 days in 1947. A total of 663 spot groups were recorded, breaking all yearly records since the catalogue of individual groups was begun at Greenwich in 1874. The previous records were 547 in 1938 and 540 in 1893.

THE GREAT MAGNETIC STORM OF MARCH 24, 1940

The greatest magnetic storm of recent years occurred on Sunday, March 24, 1940. For a few hours it completely interrupted all long-distance communication, war reports and Easter greetings alike. Had it occurred on a business day the financial loss would have been even greater with garbled stock reports adding to the confusion. A magnetic storm interrupts communication by inducing, in long telegraph and cable circuits, electric currents strong enough to change regular messages beyond recognition. Radio communication suffered in much the same way. The static was very bad and the announcers talked a language no one could understand. Only far-distant stations were affected however. Local broadcasts, which are not reflected from the ionosphere, were just as distinct as ever. The earths magnetic field at Mount Wilson was first disturbed at 10:17 p.m. on March 23 (6h 17m G.C.T.), but the storm did not begin in earnest until March 24 at 5 : 49 a.m. (13h49m G.C.T.). The most disturbed period was between 8 : 00 and 11 : 00 a.m. (15h 40ra to 18h 50m G.C.T.). The variations were so large and so rapid that the spot of light from the magnetometer sometimes moved too fast to register and occasionally was off the record. The exact range in the horizontal intensity is therefore uncertain, but at 8 : 00 a.m. it dropped in about twenty minutes from at least 200 gammas above normal to 600 below. This was a decrease of more than 3 per cent of the normal horizontal intensity on Mount Wilson, which is about 26,000 gammas (0.26 C.G.S. units). An aurora of moderate intensity was observed by Anthony Wausnock at the Mount Wilson Observatory on the night of March 24 just before moonrise (March 25, 3h SO111 G.C.T.). The aurora was not visible in the light of the moon which was one day past full phase. During March 25 the horizontal intensity was from 200 to 120 gammas below normal. On March 26 it began to recover

SOLAR ACTIVITY IN 1955

During 1955, observations of the sun were obtained at Mount Wilson on 333 days. Of the 32 completely cloudy days, only five were in the six months May through October. No spots were seen on the sun on 38 of the days on which observations were made; a long series of 20 spotless days occurred from March 9 through 28 inclusive. January 1955 was the first month in the new cycle with no spotless days ; the last month of the old cycle with no spotless days was September 1953. The total number of sunspot groups observed at Mount Wilson in 1955 was 208, compared with 46 in 1954, and 93 in 1953. Ten years ago at a similar phase in the cycle, the number of groups in 1945, 1944, and 1943 was 220, 72, and 89, respectively. The northern hemisphere was again the more active with 127 groups compared with 81 in the southern hemisphere. Two of the 208 groups certainly belonged to the old cycle, the last one having appeared on November 24. The average latitude of the new cycle groups in the northern hemisphere was 26? 6 and in the southern hemisphere 25? 1. In 1954 the corresponding latitudes were +27?7 and 26?5. Solar activity has increased during 1955 at a rate slightly greater than at the same phase in the previous cycle. This rapid increase since the minimum in April 1954 is shown in Figure 1. The first long-lived active region of the new cycle began its activity in April 1955 in latitude about 25° south. A total of eight groups, two of which were quite active, occurred in this region. Chromospheric activity was in evidence on every return from April through November. Monthly means of the number of groups observed daily at Mount Wilson in the last three years are given in Table I.

SOLAR ACTIVITY IN 1953

During 1953, observations of the sun were made at Mount Wilson on 350 days, on 109 of which no spots were seen. The fifteen completely cloudy days in 1953 were evenly distributed throughout the year, only one month having three such days and four months none. The previous record for the number of observing days per year was 341 in 1942. The longest continuous sequence of spotless days was from November 8 to December 5 inclusive. The total number of spot groups observed at Mount Wilson was 93 in 1953, compared with 219 in 1952 and 294 in 1951. Only one of the 70 groups for which magnetic polarities were determined was irregular. The northern hemisphere was slightly the more active in 1953, having 51 groups, while the southern hemisphere had 42. The average latitude of the spot groups was 9?9 for the northern hemisphere and 8?6 for the southern. This compares with 10?7 and 10?4, respectively, in 1952, and 11?6 and 11?3, respectively, in 1951. The mean latitude of 9?9 in the northern hemisphere is for spots of the waning cycle and excludes one very high-latitude, short-lived spot1 at 52° N. The low average latitude of the groups indicates that the minimum is near and that new-cycle spots should be predominant in 1954. Sunspot activity, which declined noticeably in 1953 (Fig. 1), had a small maximum in August and September. This maximum in the short-period fluctuations was about thirteen months after a similar one in 1952.2

SUNSPOT ACTIVITY DURING 1951

During the calendar year 1951, solar observations were made at Mount Wilson on 329 days, one of which, August 27, was without spots. Until August 27, the sun had not been spotless since December 22, 1950. The total number of spot groups observed in 1951 was 294, which was 83 less than in 1950. The northern hemisphere with 158 spot groups was more active than the southern with 136. Following the minimum of 1944, sunspot activity developed more rapidly in the southern hemisphere than in the northern until a maximum was reached in 1947. Activity in the northern hemisphere continued to increase until a maximum was reached in that hemisphere in 1949. Since 1949 activity has declined in both hemispheres, with the northern hemisphere the more active each year.. The average latitude of the spot groups in 1951 was 11?6 in the northern hemisphere and 11?3 in the southern. In 1950 the corresponding latitudes were N 13?9 and S 12?4. The monthly means of the number of spot groups observed daily for the last three years are shown in Table I.

Solar and magnetic data, April to September, 1947, Mount Wilson Observatory

During April (and also March) the Earths magnetic field was remarkably calm for an equinoctial month in which very large spots were present on the Sun. Although the huge complex bipolar group, No, 8478, which crossed the solar disk from March 30 to April 14, covered a large area and had complex magnetic fields, it produced only a few flares, all of those observed at Mount Wilson being small. This group, a return of the large spot of March, was the largest ever recorded, even surpassing the great group of February, 1946. The magnetic storm of April 8–9 occurred when the great group was 1.8

SUNSPOT ACTIVITY DURING 1945

During the calendar year 1945, solar observations were made at Mount Wilson on 323 days. Only 12 days were without spots, compared with 123 in 1944. The total number of sunspot groups observed in the overlapping new and old cycles was 220, compared with 72 in 1944. The number of groups belonging to the new cycle increased from 52 in 1944 to 212 in 1945 : the number in the northern hemisphere increased from 19 to 71 ; in the southern hemisphere from 33 to 141. The number of groups belonging to the waning cycle decreased from 20 in 1944 to 8 in 1945 : the number in the northern hemisphere decreased from 8 to 1 ; in the southern hemisphere from 12 to 7. The monthly means of the number of groups observed daily for the last three years are in Table I.

SOLAR ACTIVITY AT THE ECLIPSE OF JULY 9, 1945

On July 9, 1945, six groups of sunspots were visible, a very small one near the west limb and five near the east limb (Plate XII), two of which were in the northern hemisphere and three in the southern. The magnetic polarities in all the groups were normal for the present cycle, negative (S) spots preceding in the northern hemisphere and positive (N) spots preceding in the southern hemisphere. The largest, No. 7791, was a bipolar group which had come around the east limb on July 8 ; its position was 20° S, 77° E on July 9.5 G.C.T. This group, which consisted of two large spots with a few small ones between, had a total area of about 600 millionths of the visible hemisphere and a maximum field strength of 2500 gausses. It was followed closely by two small groups, Nos. 7794 and 7795. The second largest group, No. 7790, 18° N, 63° E, was also bipolar; its maximum field strength was 1900 gausses, its area about 150 millionths. A small group, No. 7793, was 3° north of it and 17° nearer the east limb. Group No. 7792, the only one not near the east limb, consisted of two tiny spots just visible in a small area of faculae at 17° N, 69° W. No abnormal activity was observed on the sun for several days before July 9. The spots were surrounded by ordinary faculae and flocculi, the prominences over them being smaller than normal. The calcium (K2) spectroheliograms on July 9 and 10 (Plate XIII) show bright flocculi in latitude 3° S (longitude 40° E on July 9), although no spots were visible there on those days. On July 6, 7, and 8, however, a group of small spots was visible in the area covered by these flocculi. The polarities as well as the low latitude of the spots identified the group as a member of the old cycle. The lack of hydrogen flocculi is well shown in Plate XIV, a. The small prominences visible on July 9 are shown in Plate XIV, b ; Table I lists the positions and heights of the largest ones. Solar activity on the day of the eclipse was normal for the

SUNSPOT ACTIVITY DURING 1943

During 1943, solar observations were made at Mount Wilson on 323 days ; forty-six days were without spots, compared with sixteen in 1942. Six groups of the new cycle, all in the southern hemisphere, were observed in 1943. In 1942 one very small bipolar group, latitude +32°, observed on December 20 only, may have been a member of the new cycle. Its polarities were like those in the present cycle but its inclination to the equator was so great, 75°, that its polarities have low weight in deciding to which cycle the group belonged. In the waning cycle, the number of groups decreased from 188 in 1942 to 89 in 1943 : the number in the northern hemisphere decreased from 93 to 54 ; in the southern hemisphere from 95 to 35. The monthly means of the number of groups observed daily for the last three years are in the following table.