PROCEEDINGS OF THE CANADIAN rNSTITUTE. 



35 



The Great Sun-Spot of September and October, 1898. Bv Andrew 

 Elyins. 



(ReaJ February iSth, iSgq.) 



The present year lias furnished us with one of the finest groups of sun-spots 

 which I have ever observed ; it has attracted the attention of observers throughout 

 the world, and I have thought, that as I observed, and made drawings of it on 

 each day when clouds did not render observation impossible, it might be of 

 sufficient importance to bring it before the Institute. 



The spot must have been on the eastern limb a day or more before I saw it. 

 My first observation was on the 4th when it was inside the limb a day, or perhaps 

 two days distance. I was struck by its large size, and the black umbra, and as I 

 thought it would be an important spot I sketched it. On the 5th the unibra was 

 seen to be comj^osed of four parts ; {as some think), formed by the photosphere 

 throwing portions of itself across the dark umbra which is regarded lower than the 

 photosphere; such divisions called " bridges " or "tongues" are seen in nearly all 

 large spots. I think they are breaks or divisions in matter lying on, or above' the 

 photosphere ; which permit the photosphere to be seen through the openings or 

 breaks. 



The spot had a small spot on the north preceding side very near the 

 penumbra of the large spot, two or three on the north following side, also very 

 near or joined to the penumbra of the large spot, and also two following between 

 the spot and the limb. 



On the 7th the umbra was greatly changed ; I could only see three dark umbra 

 divisions instead of four, the two small groups which followed on the 5th had 

 become much larger and contained many black points in a penumbral shading 

 which enclosed the whole. 



On the 8th the three umbras had disappeared, and one large black mass 

 existed in the large oval penumbra, the north preceding spot was more distant 

 from the penumbra of the large one than on the 7th, and all the following spots 

 in the train had become larger and more distinct ; there were also fragments of 

 penumbra, scattered through the intervals between the trains, larger spots, and 

 a number of black points on the photosphere too small to show any details. 



Being near the sun's central meridian I estimated its size in the following 

 manner, roughly of course, but not far from the reality. 



Sun's diameter 800,000 miles, length of group one-sixth (J) of sun's diameter, 

 = 130,000 miles, large spot about one-third of the length of group, equal 43,000 

 miles. 



An extract from a letter written September 9th by Prof. DaAid E. Iladden 

 will throw additional light just here. 



"When I first observed this spot, but a mere line of light separated it from the 

 edge of the limb, no penuml)ra being visil)le except on the north and south edges of 

 the long umbral line, (a bright aurora was seen the same evening.) On the following 

 day penumbra was visible on all sides of the umbra, . . . the changes from day 

 to day were quite marked. Owing to atmospheric conditions the spectroscope 

 could not be used until the 6th, when but little or no disturbance could be noticed 

 in the vicinity of the spot. On the 7th thougli, a sudden outburst occurred. 

 When the spectroscope was adjusted at 11.40 a.m. central time, the entire region 

 just preceding, and for some distance following, the spot was greatly agitated, the 

 Ha line being reversed and distorted, small black jets projecting from each side of 

 the line were noted in several places, and on opening the slit .slightly, the flame 

 and spike-like figure of the disturbance could be clearly seen. At 12 noon, intensely 

 Inilliant flames were observed over the large spot extruding from the umbra to the 

 umbra to the edge of the penumbra on tlie east side. This phenomenon was particu- 

 larly striking — the intensely bright scarlet flame nearly in the centre of the dark 

 absorption band of the spot spectrum being very interesting ; the Ds line was bright. 



