The Sun with giant sunspot group AR11944 (lower left) on 6 January 2014. Courtesy SDO/HMI
Solar astronomy delivers! Without warning new and strange examples of your subject appear – a gift ‘for those who would scan the face of Nature’ (as C.P Gaposchkin put it). One such unexpected ‘gift’ made its debut at the Sun’s eastern limb on Jan 1st 2014: AR11944 – a truly huge sunspot!
On Jan 1st (local 2nd) in white light, a large spot was seen, much foreshortened by our line-of-sight –located at –8,102 (i.e. 8ºS solar latitude, 102º longitude). This was followed by a scatter of mid-size ‘followers’ that seemed to stretch out of view behind the SE limb.
The main spot was 15° from the limb. Of the (f) spots seen, one was sited south of the main spot at –11,98, and a lesser one lay at –7,96, just 9º from the limb. There were vague hints of penumbrae all the way to the limb – but they were not mapped in Fig1 below. Helio freeware gave spot coordinates and an area of 800 units for the enormous group!
When such spots appear they usually have strong umbral fields: i.e. the fields define the size of the spot. The big main spot had a field of R25, i.e. 2500G magnetic flux with ‘red’ polarity; in fact most of the spots were of red polarity, see figure below. Just one of the lesser followers had an unlike field (violet 2100G). The Jan 1 session was ended by cloud – and the next day totally cloudy.
Jan 3 (local 4th) looked hopeless too, but the scope was set up – and over two hours some of the complexity of AR11944 was logged (Fig2) via cloud gaps.
A sketch of sunspot AR11944 and its associated activity. Sketch and copyright Harry Roberts ©, all rights reserved
AR11944 – White light. Over 48 hours the group had grown very complex, with two big (p) spots followed by irregular chains of smaller ones, all spread across 15º of longitude and about 8º of latitude: an exceptionally large group! The most eastern spot, captioned (f) in Fig2, was sited at –8,90, the great (p) spot at –8,103. The group’s area was hard to calculate but “Helio” gave ~1400 units, a McIntosh Class Fkc: a real giant! The sketch shows only a general outline of the many lesser spots.
AR11944 in H-alpha. In this band the group had even greater complexity –mainly due to the many curious dark filaments (arf) that emanated from or converged to the big (p) spots in a magnetic spiral: like an H-alpha ‘twister’. I can’t recall anything comparable in SC24. Spot fields often emerge from major spots in a spiral and it’s assumed to be the case here, but rarely in such profusion: super-group AR10652 in 2004 comes to mind.
Most of the dark features were true filaments – but filter tuning suggested a-a1 was in fact a surge. Off-band tuning showed the filament darker at points along its length, suggesting surge material emerging at point a and moving to a1. The curved feature b is also a surge, I suggest.
Surges often seem to occupy filament channels – at least temporarily. The ejection and retraction of surge material along a pre-existing filament seems to leave the filament unaffected after the event. Perhaps this was happening here. Other active region filaments threaded their way between the chains of lesser spots.
Plage and a flare. Extensive plage threaded around the periphery of many spots –shown white in Fig2. An M1.1 flare had erupted at the (p) end of the group fifteen minutes before viewing began. However X-ray flux remained high throughout, and at 22:50 was at GOES C1, with areas of flare brightness shown red in Fig2.
Ejecta. At 23:01 a dark globule of material was seen with a strong blue-shift (Fig2 arrowed) and is assumed to be the ejecta from the C1 flare; it was moving in the direction of the arrow.
Filament motion. The small filament arf1 just above the main spot is show at 22:53 – but was in motion too and reached the dotted position by 23:20 – perhaps a filament ejection. It and the larger filament to the north seemed to merge ~23:30.
Polarity prognosis. This group will dominate the solar landscape for days to come; will its fields strengthen? It has had several class-M flares and will have more. However, its polarity is Hale Class Beta-Gamma: the suggested inversion line is dotted in Fig2 – a simple separation of polarities. There is no sign YET of opposite polarities within one penumbra (Hale Delta class) – though that can happen overnight! If it does, there will be major flares.
Stay posted! And take a look: even a modest scope with a suitable filter will show this ‘giant’, and in H-alpha there may well be fireworks!
Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers.