224 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Sept., 1905. 



Stscr MsLp.— No. 4. 



Perseus. Aviriga, and Taurus. 



The fxjrtion of the heavens here represented is one full of 

 interest. In addition to the three well-known constella- 

 tions named, we have the greater part of Orion, which 

 forms one of the most conspicuous and easily recognised 

 of all the constellations, as well as Gemini (the greater 

 part of which has appeared in Map No. 6). 



Orion is one of the useful star figures by which one's 

 position is readily ascertained. The three stars forming 

 the head are due north of the centre of the belt. The 

 sword depending from the belt is an appropriate sign of 

 the N. and S. line +. 



The Great Nebula^ of Orion, situated in the centre of 

 the sword, is certainly one of the most remarkable objects 

 in the heavens. This nebula', visible to the naked eye, and 

 presenting a wonderful appearance on the photographic 

 plate, seems to be but the centre of a huge spiral which 

 extends faintly on all sides to the limits of the con- 

 stellation. 



There are a number of conspicuous stars in this part 

 of the sky. 



e Persei (II. h. 37 m. + 48' 49') is a triple star, of 

 which two, A and B, are probably binaries, while C at a 

 distance of 80" does not share the same proper motion, 

 and is, therefore, probably independent. 



^ Persei (Algol) (III. h. 2 m. -f- 40° 35'). This star has 

 long been known as an e.xtraordinary variable, hence 

 called El Goiil, " the demon." It has a regular period of 

 variability. After being for 2 days 21 hours of 2-2 mag- 

 nitude, it rapidly declines, until in just over four hours it 

 is only yj magnitude, after which it increases again in 

 about the same time to its original magnitude. It is now 

 practically certain that this change is caused by the in- 

 terposition of a large dark body revolving around the 

 brighter one, the orbit of w-hich happens to be in a plane 

 which passes through our earth. The two stars are 

 probably very close together, and of much the same size. 

 On September 3 it is at its minimum at 4 h. 42 m. a.m., 

 from which time the other phases can be calculated. 



The Pleiades {Wl.h. ^1 m. + 23^48'). This well-known 

 cluster contains si.x stars visible to the naked eye. As 

 most of them have a common proper motion, they doubt- 

 less form a system. A nebulosity surrounds all the prin- 

 cipal stars. The length from Atlas to Celano is 1 ' 6'. 

 Those who have not considered the matter are ofien sur- 

 prised to hear that this little group covers an apparent 

 area much greater than that of the I'ull Moon (the mean 

 diameter of which is 31'), and a representation to scale is 

 therefore appended. 



o Tauri (Aldebaran) (I\'. h. 30 m. + ifp 19'). Magni- 

 tude, ri. Near this is the group known as the 

 " Hyades." 



On Jreptember 19 the Moon will pass across the region 

 of the Hyades and Aldebaran. (Vide p. 236.) 



a Auriga {Capella) {\ . h. 9 m. + 45^54'). Magnitude, 

 02. 



ft Orionis {Rigel) (V. h. 10 m. — 8*^ 19'). Magnitude, 

 0-3. 



Nebula M. 1. Tauri (V. h. 29 m. + ai'-' 57'). Known 

 as the " Crab." 



Orionis (V. h. 29 m. — 5'' aS*). A multiple star situ- 

 ated in the Great Nebula of Orion. Four principal stars 

 are of magnitudes 6, 7, 7J, and 8. 



a Ononis (V. h. 34 m. — 2° yj). A multiple, com- 

 poied of two sets of treble stars. 



{ Orionis (V. h. 36 m. — 2^ o'). A double star, magni- 



tudes 2 and 6, with a faint companion 57" distant of loth 

 magnitude. 



a Orionis (Belelgiiese) (W h. 50 m. -f 7° 23'). A yel- 

 lowish-red star, 1st magnitude. \'ariable to a slight 

 extent. 



^Auriga {Menkalinan) (V. h. 52 m. + 44° 56'). A 

 spectroscopic binary, proving it to consist of two equally 

 bright stars revolving in a period of 4 days. 



The 



Great Sovith Tropical 

 Spot on Jupiter. 



One of the most interesting and prominent features 

 of Jupiter during the last four years has been a dark 

 shading spreading more or less over the south tropical 

 zone. It has been visible since the spring of 1901, and 

 has maintained so striking an aspect, albeit a change- 

 able one, that it promises to offer a parallel with the 

 red spot and its surroundings as regards permanency. 



Though situated in the south tropical zone of the 

 planet its motion accords with that of the south tem- 

 perate current which is about 9 h. 55 m. 19 s. from a 

 mean of many spots seen at Bristol in recent years. 



Between June 18th, 1901, and August 7th, 1905, the 

 spot completed 3,655 rotations, with a mean period 

 of 9 h. 55 m. 18.9 s., and it lost 16°. 2 of longitude 

 per month relatively to system II. (based on a rate of 

 9 h. 55 m. 40.63 s.) of Crommt'lin's cphemeride-s. 

 The motion appears to have become gradually slower 

 with the time, the rotation period having been about 

 9 h. 55 m. 18.5 s. in 1901, whereas it was about 

 9 h. 5.S m- 19-55. in 1905. 



In 1903 the average length of the spot was 48°, but 

 when passing the red spot in July, 1902, it was about 

 87° long. I obtained an observation of the object on 

 August 7th, 1905, as under : — 



u. M. Longitude. 



.So the length on that occasion was=4j'^.5. I used 

 a i2i-in. Calver reflector, powers 300 and 440, but the 

 latter was rather too high for the state of the air. 



The durablcness of this marking, its conspicuous ap- 

 pearance, and the fact that it has apparently influenced 

 the very irregular motion of the rod spot in and since 

 1901, render it a peculiarly important and attractive 

 object for telescopic observers. It should be looked for 

 in the following' longitudes duriiii,"- tlie next two years : — 



Date. 



1905. September 15 



October 15 



,, November 15 



December 15 



igo6. January 15 



Fel)ruary 15 



April 15 



August 15 



,, October 15 



December 15 



igoy. February 15 



April 15 



,, September 15 



Bristol, August 8, 1905. 



Longitude. 



158K 



142-6 



1264 



iro-2 



940 



778 



454 



340-6 



. . 308 2 



.. 2758 



243'4 



2 1 I 'O 



1300 



W. I'. Denni.nc. 



