52 



ASTRONOMICAL PROGRESS IN 1898. 



ring system is always eccentric to the globe, nearer 

 west tiiiin fast that" is, the eastern vacuity is greater 

 than tin- western. Two sets of accordant measures 

 gave 4.3" for the distance separating tho planet's 

 limb from the inner edge of ring U. and 4.0' for the 

 corresponding distances of the west. Several ob- 

 Berren declare they have seen the middle ring divid- 

 ed as distinctly as the visibility of Encke's division 

 of the outer ring. By one astronomer the middle 

 ring was seen divided into three parts. The inner 

 ring was exceedingly faint, but was seen separate 

 from ring B by a distinct shading. The planet was 

 seen clearly through the crane ring (C), and the 

 shadow on the globe sharply defined with no irreg- 

 ularities. 



Planetary Magnitudes. At length we doubt- 

 less have the diameters of the planets and their 

 satellites more accurately determined than has here- 

 to fore been possible. Dr. E. E. Barnard, at the Lick 

 rvatory. made an extensive series of micromet- 

 rical measurements, lately published, of all the 

 planets and some of the satellites. They were all 

 made with the 36-inch telescope, except those of 

 Mercury, which were made while he was transiting 

 the Sun with the 12-inch telescope contracted to 

 4 and 5 inches. To be as brief as possible, their 

 dimensions arc given in miles only : Mercury, 

 2,765 miles ; Venus, 7,826 ; Mars, equatorial, 4,352 ; 

 Mars, polar, 4,312; Mars's spheroidity, 40; Jupiter, 

 equatorial, 90,190; Jupiter, polar, 84,570; Jupiter's 

 spheroidity, 5,620 ; Saturn, equatorial, 76,470 ; Sat- 

 urn, polar, 69,780; Saturn's spheroidity, 6,690; 

 outer diameter of ring A, 172,610; inner diameter 

 of ring A, 150,480; outer diameter of ring B, 145,- 

 990; inner diameter of ring B, 110,070; space 

 between rings A and B, 2,245; inner diameter of 

 crape ring, 88,190: Uranus, diameter, 34.1)00; Nep- 

 tune, diameter, 32,900. Satellites : Jupiter No. I, 

 2.452 miles ; Jupiter No. II, 2,045 ; Jupiter No. Ill, 

 3,558 ; Jupiter No. IV, 3,445 : Saturn's Titan, 3,720. 

 Afifi-roids: Ceres, 485 miles; Pallas, 304; Vesta, 

 243; Juno, 118. 



Stellar Parallax. Dr. Gill, from observations 

 made at the Cape of Good Hope Observatory, con- 

 cludes that the parallax of Alpha Cehtauri is certain- 

 ly between 0.74" and 0.75", and that of Beta Otionis 

 (Uigel) is not greater than 0.01". He finds that of 

 Alpha Gruis to be 0.015". It is perhaps needless to 

 notify the reader that but little credence can be 

 given to measurements so minute as the last. M. 

 HolTler finds the mean distance of Beta, Gamma, 

 Delia, Kpsilon, and Zeta Ursa? Majoris (five of the 

 seven stars forming the Great Dipper) is four million 

 timrsthat between the Karth and the Sun ; and that 

 Kpsilon is forty times brighter intrinsically than the 

 dog star. 



Proper Motion of Stars. Dr. Capteyn recently 

 discovered a star that has a larger proper motion 

 than has (Jroombridge 1830, which heretofore has 

 been considered the most rapid known, and has 

 been called I lie "runaway star." Capteyn's star is 

 in the Cordoba Zone Catalogue, where its place is 

 given as right ascension 5 h 6 40.61"; declination 

 south 44 58.176', for the epoch of 1873. He de- 

 duces an annual proper motion for it of 8.707", while 

 that for Groombridge 1830 is but 6.723", or nearly 

 two seconds greater. The star is of the ninth mag'- 

 nitude, much fainter than the Groombridge star. 



Discovery of Nebulae. Since Dr. Lewis Swift, 

 with his astronomical instruments, removed from 

 the Warner Observatory, at Rochester, N. Y., to the 

 Lowe observatory, at Kcho Mountain, California, 

 he has devoted his time to the discovery of nebula? 

 and comets. In the past three and a half years 

 he has discovered 6 comets, and more than 300 

 nebula', nearlv all southern. The " Astronoinischc 

 Naehrichtcn," No. 3517, published at Kiel, Germany, 



contains a catalogue of 243 of the nebula? discovered 

 at Lowe Observatory, with a description of each, 

 and several notes. They are mostly very faint. A 

 few are very interesting. From his low latitude. 

 34 20' north, he has a great advantage over most 

 other northern observatories. Besides this, the 

 number of clear nights is out of all proportion to 

 those enjoyed elsewhere. In July, 1897, there were 

 31 clear nights, and in August 29, ard during the 

 year 299 nights were clear, 25 partly clear, and 41 

 cloudy. One of the nebula- is a nebulous star of the 

 eighth magnitude in the center of a round, sharply 

 defined nebulous atmosphere. Two were line nelm- 

 \n\ which must be either rings or flat disks, with 

 their edges parallel to the line of sight. The ring 

 nebula in Lyra is perpendicular to the line of sight. 

 This remarkable object was discovered in 1779 in 

 France, by Darquier. The spectrum shows it to be 

 composed wholly of gas, without a star. Between 

 us and it or beyond, we know not which, is a central 

 star of unimagined faintness. On it and within it 

 the great Lick telescope shows 11 stars besides the 

 central one. 



Astronomical Constants. The exact value of 

 the astronomical constants precession, aberration, 

 and nutation has ever been disputed, and lately 

 the question has assumed the dignity of internation- 

 al importance. For many years prior to A. D. 1900 

 the value given in the "American Nautical Almanac" 

 to precession of the equinoxes was 50.2411" + 

 0.0002268*, for nutation 9.2231" + 0.000009/, in which 

 t is the number of years since A. D. 1800. and to ab- 

 erration 20.4451". As the evidence appeared strong 

 that they were slightly erroneous, Prof. William 

 Harkness, who is now its director, has for the "Alma- 

 nac " for A. D. 1900 changed those constants as follow : 

 Precession to 50.2482" + 0.00022*, nutation to 9.21", 

 and aberration to 20.47", and mean obliquity of the 

 ecliptic to 23 27' 8.26". Aberration is the displace- 

 ment of a star by the Earth's orbital motion com- 

 bined with the motion of light. It therefore follows 

 that if the velocity of light be known, and the 

 amount of aberration with exactness, the most ele- 

 mentary mathematical calculation will determine 

 not only the rate of motion of the Earth in its orbit, 

 but its circumference also and the radius, and 

 finally the solar parallax itself. The velocity of 

 light is considered to be accurately known ; and 

 were the value of the aberration equally trustworthy 

 this method of obtaining the parallax of the Sun 

 would be one of the most exact and convenient we 

 possess. Unfortunately this, like all the other pro- 

 cesses for obtaining the Earth's distance from the 

 Sun, has a slight uncertainty, which until recently 

 was supposed not to exist. Prof. Doberck, of the 

 Hong-Kong Observatory, has introduced a very ex- 

 traordinary element of doubt into the problem by 

 discovering that the value of the aberration con- 

 stant decreases with the decrease of the magnitudes 

 of the stars observed. For instance, when the 

 average magnitude of the stars observed was 4-jV the 

 constant came out 20.639"; with stars of 5 fa mag- 

 nitude it became 20.430", and with 6^ it was only 

 20.385". The almost inconceivable variation, as in- 

 dicated above, entails a vast difference in the SunV 

 distance from the Earth, showing that it may be 

 it her 93,641,600 miles, 92,093.300 miles, or only 

 92,489,100 miles. Prof. Doberck is cf the opinion 

 that the constant of aberration thus found to de- 

 pend on the magnitude of the stars observed may 

 reconcile the differences in the values obtained at 

 different observatories. 



Variable Stars. The discovery of stars that 

 vary in brightness has made much advancement 

 during the past few years. The number of astron- 

 omers, and especially of amateurs, engaged in their 

 detection and the law of their variation is very 





