Sunspot group AR 11515 on 30 June (UT) and 2 July 2012. Sketches and copyright Harry Roberts ©, all rights reserved

Recent signs of stronger activity in the sun’s south, hitherto notably quiet, were boosted by the arrival of June’s large group: AR11504 – the first large southern group for solar cycle 24 (SC24). As reported earlier, it rotated out of view about June 23 – leaving an almost blank disc.

After a few days of cloud and rain the next large southern group emerged in the sun’s east: AR11515. This was to reach 1000 units in area and underwent some unique evolutions before keeping its date with the sun’s SW limb.

I first logged it on June 30 (Fig) a Hale beta-class group with a large preceding (p) spot and a trio of follower (f) spots. It seemed a simple enough bipolar group, though fairly large in area (350 units) and already stretched across ten degrees of longitude.

The (p) spot had a cluster of tiny ‘satellites’ within its large penumbra, but fields (© Regents of University of California, Mt. Wilson) were modest: red 2000G (R20) in the main (p) spot and R14 in its ‘satellites’. These seemed to be dividing from the (p) spot, however. This vague hint in the preceding spots was the only warning of rapid changes over the next week or so.

Flares are caused by the emergence of new flux or sunspot motion resulting from the new flux: this would now be dramatically demonstrated.

The top part of the above Fig shows big changes in just two days: the ‘satellites’ split from the round (p) spot and spread southwards – while the (p) itself began to expand in E-W direction, briefly showing four umbrae in the one penumbra with two light-bridges (LB) on Jul 2nd – and shaped like an egg-plant.

But this was a brief configuration: within a day the elongated (p) spot had split into two irregular components, while the ‘satellites’ developed their own penumbrae.

The writer kept attention of the multiple (p) spots, but the following spots also developed into spot chains with very irregular penumbrae – a sign of complex fields. Soon the group was almost 15º in longitude length (LL15).

All this motion and new flux meant multiple GOES M-class flares: eight on 4th July and nine on the 5th! These flares were all short-lived events however. Finally, on July 6 at 23:08 a GOES X1.1 erupted.

During its transit of the sun’s disc AR11515 was preceded by a sparse active region AR11514, and the two could be seen interconnecting fields in SDO EUV imagery: so several strong flares have been attributed to 11514. This includes the X1.1 – that erupted between the two groups – showing the challenges of interpreting solar activity.

Sunspot group AR 11515 on 3 & 8 July 2012 (UT). Sketches and copyright Harry Roberts ©, all rights reserved

Surges: One of my favourite solar features are these exotic ‘recoiling’ ejections and the view, July 3, showed repeated surges from the leading (p) spot (let’s call it pp for clarity). In the case of 11515 the single preceding spot had split into several (p) spots, and the one in front (pp) now pushed forwards, almost leaving the rest behind!

Fig 2 (lhs) shows the serpentine surges radiating from the fast-moving (pp) spot – perhaps its motion somehow caused the short burst of surging, a web search showed they were all over in a few hours. The sketch shows several surges logged over a 2-hour period.

Runaway: The ‘runaway’ (pp) spot pushed forward over the next 5 days, and when the group neared the SW limb (Fig 2, rhs) the (pp) spot was 5º ahead of the central (p) spot. Both (pp) and (p) were of red polarity and identical in strength. The (pp) spot now looked like another spot group ahead of 11515 – while the (p) spot and the (f) spot looked like a complex beta class spot group. Very confusing!

What caused the strange ‘runaway’ spot? I would like to know. The position of the individual spots within the group showed it was now more than 15º in LL – a very long group – and its area probably exceeded 1000units.

All those M-class flares and the one X-class (if it is counted as part of 11515, rather than 11514) should put 11515 into the list of largest southern group so far, and the one with the strongest flares.

Stand-by sun-watchers, there may be more unusual groups soon to emerge around the sun’s eastern limb!

Harry Roberts is a Sun and Moon observer, a regular contributor to the Sydney Observatory blog and a member of the Sydney City Skywatchers