NOTES. 



ASTRONOMY. 



By .A. C. D. Crommelin, B.A., D.Sc, F.K.A.S. 



THE ECLIPSE OF THE SUN, APRIL 17th.— Fine 

 weather favoured this phenomenon all along the central line, 

 and the spectacle was enjoyed by a large number of visitors 

 from this country. It was known in advance that only the 

 most fleeting glimpse of the corona could be expected ; this 

 was obtained by a few, including Professor Turner. In 

 Portugal. Mr. Worthington saw it for several seconds, and 

 was able to note that it was of tlie " wind-vane " type 

 associated with spot-minimum. Mr. Slater succeeded in 

 photographing it. 



The duration of totality in Portugal given by The Nautical 

 Almanac ihalf a second) was verified, thus showing that the 

 diameter of the Moon used for eclipses is correct. .■Vs regards 

 the position of the central line, the American Ephemeris is 

 to be congratulated on its successful prediction. It applied 

 + 9"-S, +l"-7 to the calculated longitude and latitude of the 

 Moon, the result showing that these corrections were very 

 nearly right, but probably that in longitude should be slightly 

 increased, and that in latitude diminished. Our Nautical 

 Almanac and the German one did not attempt to correct the 

 Moon's place, and their tracks were two or three miles too far 

 to the N.W. : the French one corrected the Moon's R.A. but 

 not her Dec. and its track was a mile and a half too far S.E. 



The eclipse near Paris was neither total nor annular, though 

 many observers erroneously used the latter term. .An annulus 

 means an unbroken ring. I observed by projection on a 

 white screen, thus reducing irradiation, and 1 can say with 

 confidence that there was not a continuous ring of sunlight, 

 but only disconnected patches in the depressed parts of the 

 Moon's limb. Baily's Beads were beautifully seen. 



The light at mid-eclipse grew quite dim, and of a weird 

 reddish or purplish tinge. M. Antoniadi ascribed this to the 

 fact that we were only receiving light from the extreme edge 

 of the Sun, which has to traverse a great extent of solar 

 atmosphere, most of the blue light being ab.sorbed. 



M. and Mine, .\ntoniadi made interesting observations of 

 the shadow bands, which they describe as wriggling snakes 

 moving rapidly in the direction of their own length in a 

 direction nearly away from the Sun, i.e., from S.S.W. to 

 N.N'.E. (this was also the direction of the wind) at a speed 

 about equal to that of a running man. In most eclipses the 

 motion of the bands has been transverse to their length. 



THE INTERESTING MINOR PLANET M.T. — The 

 discovery and loss last October of this interesting body will 

 be remembered. It was discovered by Dr. Palisa at Vienna, 

 and was remarkable for the fact that, although in opposition, it 

 was advancing pretty rapidly in R..^. Hence its orbit is 

 evidently highly eccentric. There is not really enough obser- 

 vational material to determine the orbit, the following four 

 positions being all that are available ; the first two were made 

 by Palisa at Vienna, the others by Pcchule at Copenhagen : — ' 

 Local ^^T. .\pparent. R..\. .Apparent. Dec. 



1911. 

 Oct. 3* 14" 51" 56"- ... 0''42"' 4''-83 ... N.O" 15' 40"-8 

 „ 4 10 4t) 41 -3 ... 43 43 -30 ... S. 12 48 -9 

 .. 4 14 n 3-0 ... 43 58-99 ... S.O 17 50-8 

 ,. 4 15 7 5-0 ... 44 3-14 ... S.O 19 12-5 

 With this material two independent determinations of the 

 orbit have been made; the first by E. S. H.aynes and J. H. 

 Pitman in Lick Bulletin, No. 210, the second by Dr. Franz 

 in Astr. Nadir., 4571. The first seems entitled to rather 

 more confidence from the more reasonable values of the 

 eccentricity and period : there is one point in favour of 

 Franz's orbit, viz.. it makes the diminution of brightness more 

 rapid, which would explain the failure to recover the planet 

 towards the end of October. ^It will be seen that the node, 

 inclination, time of perihelion, and perihelion distance are 



known within fairly narrow limits, but that the eccentricity 

 and period are subject to great uncertainty. Both the orbits 

 are referred to the ecliptic and equinox of 1911 -0. 



Lick Orbit. Franz Orbit. 



T 1911 Aug. 20-748 G.M.T. Aug. 15097 G.M.T. 



" 141° 20' 27" ... ... 127° 37' 39" 



SI 185 35 59 185 54 27 



' 9 31 23 11 28 42 



« 0-50937 .. 0-S153 



f 1050"- I ... 2S3"-8 



a 2-2518 5-387 



Period ...3-379 years 12-50 years 



q 1-1048" 0-995 



Aphn. dist... 3-3988 9-779 



Both orbits make the brightness a maximum a month before 

 discovery, when it was probably of the tenth magnitude, and 

 being in high north declination there is still a chance that 

 some further images may be found on photographs in 

 September or October. The ephemeris from the Lick orbit 

 is given to illustrate the curious motion of such an eccentric 

 body when near the earth. It is for Greenwich midnight. 



Dist. from 



1911. R.A. Dec. Earth Mag. 



Sept. 1 22''15'"-8 ... 31° 3' N ... -1318 ... 10-7 



9 23 11 -1 ... 22 45 ... -1359 ... 



,. 17 2i 53 -2 ... 13 44 ... -1515 ... 11-1 



.. 25 22 -4 ... 6 ... -1779 ... 



Oct. 3 42 -0 ... 19 N ... -2140 ... 12-0 



.. 11 55 -2 ... 3 29 S ... -2585 ... 



.. 19 1 4 -6 ... 5 47 ... -3112 ... 12-9 



., 27 1 12 -0 ... 6 56 ... -3718 ... 



Nov. 4 1 IS -7 ... 7 15 ... -4403 ... 13-8 



„ 12 1 25 -2 ... 6 58 ... -5167 ... 



!, 20 1 32 -0 ... 6 15 S ... -6010 ... 14-6 



With the aid of this ephemeris. images of the planet have 

 just been found on three plates taken at Greenwich on October 

 1 1th. These will enable a more reliable orbit to be calculated : 

 there h.is not been time to do this yet. The observed R..A. is 

 32 sec. greater than the ephemeris, the observed Dec. ll' 25" 

 south. It would seem that the eccentricity is smaller even 

 than the Lick value. 



ROT.VTION OF URANUS.— The extreme ditTicuhy of 

 ascertaining the period of rotation of Uranus by direct 

 observation of the disc is well known, as spots are rarely seen, 

 and when seen they are usually of a belt character, giving no 

 definite point to select. In the March number I described 

 Professor Bergstrand's attempt to determine it by the motion 

 of the peri-uranium of the nearest satellite, Ariel. He gave 

 the rather wide range of 11 -3 to 17-6 hours, thinking thirteen 

 hours the most probable. 



At the May meeting of the Royal Astronomical Society, 

 Professor P. Lowell exhibited and described a beautiful series 

 of photographs of the spectrum of Uranus, taken by Mr. 

 Slipher at the Flagstaff" Observatory. It is only in the last 

 few years that the position of Uranus has made the application 

 of the method possible, as before that its pole (assumed to be 

 coincident with the pole of the orbit-pl.ine of the satellites) 

 had been for several years nearly central in the disc, so that 

 there was no rotational movement in the line of sight. The 

 slit was placed in the direction that would produce the maximum 

 inclination of the spectral lines as compared with those of the 

 comparison spectrum, and the inclination obtained is quite 

 obvious to the eye, and fully ten times the estimated probable 

 error of a determination of inclination for one line. Several 

 lines were measured, and the result deduced that Uranus 

 rotates in a retrograde direction in a period of ten and three- 

 quarter hours. This is quite a reasonable result, being near 

 Bergstrand's lower limit, and we may take it as by far the 

 most reliable value yet obtained. See's estimate of lO"" 7"" 

 was in tolerable accordance with it. We may hope that the 

 spectroscopic method will be applied to Neptune also. 



