What is it that causes some spots to grow very large? All are shaped by magnetic fields – stronger fields make bigger darker spots – but is this the sole reason? Why is the Sun’s magnetic flux so unevenly distributed?
Return of AR12172? It seems that 2192 (shorter #) was the return of 2172: the coordinates of the two groups show that the (p) spot of 2172 was at –11,242 and the huge (f) spot of 2192 is in the same place, at –13, 242.
However, the polarities of the two spots are opposite: the former (p) spot was red 2400G (R24) and the huge (f) spot now at the same site was violet 2700G (V27). How to explain the changed polarities? It seems some curious sunspot motions have taken place and/or new flux has emerged within the remains of the old 2172 bipolar group. More study is needed.
Indeed, as 1272 transited the western hemisphere, back in late September, we saw new flux emerge ‘ahead’ and south of the (p) spot, peppering a vast area with minor spots. Was this the genesis of 2192?
In any event, Oct. 15 showed no sign of the old group yet, but GOES reported strong flares just behind the eastern limb at 10ºS. As well, in H-alpha there were sure signs of an active group approaching (Fig1) with surges and post flare loops above the limb.
12192 emergence. Oct. 17 (Fig2) saw a big new group rounding the limb and it seemed unusually ‘bulky’: Helio freeware gave the newcomer an unlikely area of 1700 units! Surely, I had made some mistake?
The new group seemed to have minor (p) spots scattered over a large area some 8º ahead of the dominant spot, the latter sited at –13,242. In H-alpha bright plage and dark surges on the disc with a few bits above the limb, were minor signs of activity.
Area. Next day the real bulk of the newcomer was obvious (Fig3): this time ‘helio’ gave the area as 1900 units. Again I doubted my maths as NOAA had it at just a few hundred units. However, by the 20th NOAA and I were in agreement with an area of just on 2000units. Clearly this was a giant sunspot (Figs 4 and 5) and its area peaked, it seems, at 2740 units on 23rd at 2400UT – followed by a slow decline as the penumbrae of the (p) spots began to fragment
12th Biggest? How does this group compare with earlier sunspots? According to the assiduous J. Janssens, this is the 12th largest sunspot since area records began in 1874: it’s really big!
Interestingly, his data show that the biggest sunspots for the period occurred in the mid 20thC and also that 2192 was bigger than any SC23 spots. (Caution: the data are sorted by Greenwich Area not NOAA Area.)
Delta class. A very complex inversion line, the boundary between spots of opposite sign, is added in blue Fig4: source SDO. The group is of Hale Delta class, with spots of opposite sign in the same penumbrae; a merging of multiple spot groups perhaps.
- Despite its apparent magnetic complexity it did not host record flares. GOES X-class flares began, it seems, with an X1.1 Oct. 19, 05:00UT, for a total of six during disc transit. The writer logged an M8.7 and an X3.1 (more on these shortly). Surprisingly it is reported that no CME’s resulted from any of these flares. Why?
Surges. These relatively ‘cool’ jets of material that emerge from dominant spots began to appear in numbers from the big (f) spot on the 22nd. Some reached enormous lengths (23rd) before recoiling back to their starting points. More on these when we examine the group’s transit of the Sun’s western hemisphere.
This group will return after its transit of the far side: anyone with a solar telescope should look for it at the Sun’s following (i.e. eastern) limb around November 12th. Clear skies!
Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.