July, 1905.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



157 



ASTR.ONOMICAL. 



By Charles P. Butler, A.R.C.Sc. (Lond.), F.R.P.S. 



Further Notes on Jupiter's Sixth and 

 Seventh Satellites. 



Professor Peukinic, the discoverer of these two new satellites, 

 has recently published a short raiime of their features as at 

 present determined. He makes the interesting suggestion 

 that the large inclinations of the orbits of both satellites to the 

 plane of the planet's equator may be an indication that these 

 bodies have not always belonged to Jupiter, but that they may 

 be captures. 



Sixt/i Satellite. — Owing to its brightness this has been 

 readily photographed in ten minutes with the Crossley re- 

 flector, and plates have been obtained on thirty-six nights, the 

 last date of observation being March 22, as the planet is now 

 too near the sun for the satellite to be examined. 



A preliminary examination of the orbital elements shows 

 the inclination to the ecliptic and the planet's equator to be 

 about 30°. The period is probably about 250 days, with a 

 mean distance from the primary of about 7,000,000 miles ; but 

 it is not yet possible to say with certainty what is the direction 

 of the orbital motion. The actual diameter cannot be mea- 

 sured, but the determinations of brightness indicate a diameter 

 of 100 miles or less. 



Seventh Satellite. — A minute examination of negatives of the 

 sixth satellite, taken with the Crossley reflector in 1905, 

 January 2, 3, 4, showed the presence of a much fainter object, 

 which apparently belongs to Jupiter. It was at that time to 

 the N.W. of Jupiter, and had a motion towards the planet. 



The many difficultios which presented themselves in deter- 

 mining the true character of the sixth were still greater in the 

 case of this newer one. Being so much fainter, the observa- 

 tions were more difficult to secure, owing to the long exposures 

 required, and its motion was likewise harder to interpret. It 

 was considered, however, that the determinations of Feb- 

 ruary 21 and 22 made it clear that it belonged to Jupiter. 

 The seventh satellite is not shown on the negatives taken 

 during December, 1904, as it was just outside the field then 

 under observation. Definite measures have been secured on 

 the results of 20 nights, the last of which was March 9. 



A preliminar}' investigation shows the orbit to be quite 

 eccentric, the mean distance from Jupiter being about 

 6,000,000 miles, with a period of about 200 days. 



The orbit is inclined to the plane of Jupiter's equator at an 

 angle of about 30', but the direction of motion is at present 

 uncertain. Its photographic magnitude is estimated to be 

 not greater than the 16th. From this fact and a comparison 

 with the other satellites and the asteroids it is probable that 

 the seventh satellite has a diameter of about 35 miles. 



A ProbsLble New Star, R.S. Ophiuchi- 



In a special communication from the Harvard College Ob- 

 servatory Professor E. C. Pickering draws attention to further 

 observations of this so-called variable star, which shows cer- 

 tain peculiarities similar to those seen in novze. 



New stars can be distinguished from variables, in many 

 cases, only by their spectra. The usual life of a new star is 

 marked by its sudden appearance where no star is previously 

 known to have existed, and a gradual fading away during which 

 it changes into a gaseous nebula. T Coronje, Nova Persei, P 

 Cygni, and i) Carinas are instances of varied development. 



It is found that on July 15, 1898, the spectrum of the star 

 R.S. Ophiuchi was of the third type, in which the Hydrogen 

 lines H^, H7, H5, Ht, Hi were bright, and also two lines which 

 appear to coincide with the bright bands in the spectrum of 



7 Velorum at \ 4656 and X 4691. This spectrum, therefore, 

 closely resembles that of Nova Sagittarii, and also of Nova 

 (ieminorum. A photograph taken on July 14, 1898, confirms 

 the presence of the bright lines, while another taken on 

 August 28, 1894, showed that at that time the spectrum was of 

 Class K, with no evidence of bright lines. 



From an examination of the photometric light curve of the 

 star it was noticed that there was a remarkable increase during 

 the year i8g8. Before 1891 the magnitude, as determined 

 photographically, was io'9 ; it then increased gradually about 

 half a magnitude to 10-4 in 1893, and retained this until 1897. 

 In 1898 it was at first faint (io'8) until May 31. A month 

 later, on June 30, it was 77, more than three magnitudes 

 brighter, and after that it decreased regularly about a magni- 

 tude a month until October 8, when it again reached the value 

 i0'8. The following year, 1899,11 remained faint at io"6, but 

 in April, 1900, it again brightened to 9^3, diminishing to lo'o in 

 September of that year. Since then the variations have been 

 only slight. 



An examination of several good chart plates shows only one 

 star in this position, and both the spectrum and light curves 

 thus indicate that this object should be regarded as a nova 

 rather than a variable star. In this case its proper designa- 

 tion would be Nova Ophiuchi No. 3, the new stars of 1O04 and 

 1848 having also appeared in the same constellation. 



Observations of Heliunn Absorption in 

 the Sola.r Spectrum. 



The number of occasions on which reliable observations 

 have been made of the absorption spectrum of helium in the 

 solar spectrum are so few that considerable importance must 

 be attached to all authenticated instances. Probably the first 

 recorded determination was that by Young on 22nd September, 

 1870. A few months ago a paper was read before the Royal 

 Astronomical Society by Professor A. Fowler, in which he 

 recorded having distinctly seen the dark D^line of Helium in 

 the neighbourhood of the great sunspot of February, 1905. 



Quite recently Dr. H. Kreussler, of Berlin, has published an 

 account of twogood observations of thephenomenon, obtained 

 on the lathand 13th June, 1904. The instrument used was a 

 fi-inch reflecting telescope, with a spectroscope magnifying 8 

 diameters, the slit being in the region of the penumbra of a 

 large spot. It was noticed that the faculze surroundirgthe mn- 

 spots were very bright on both days. 



He suggests that the present appearance of this peculiarity, 

 considered with the above - mentioned observation of Pro- 

 fessor Young, appears to indicate that the phenomenon may 

 be characteristic of the period of maximum sunspot 

 activity. 



Comet 1905 (a). 



The following elliptic elements for the orbit of the Comet 

 1905 (a) have been determined by Herr A. Wedemeyer from 

 a computation of the observations obtained on March 26 at 

 Nice, and on April 8, 28, at Vienna : — 



EpHEMERIS for 12 H. BERLIN MeAN TlME. 



