The movement of the runaway spot from the AR11515 sunspot group. Sketch and copyright Harry Roberts ©, all rights reserved

When sunspots run away where do they go? Well, this one did the obvious thing: it went west, young man! Two weeks ago in a report on this unusual group AR11515 I wrote:

Runaway: The ‘runaway’ (pp) spot pushed forward over the next 5 days, and when the group neared the SW limb 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) spots looked like a complex beta class spot group. Very confusing!

What caused the strange ‘runaway’ spot? I would like to know.

Two weeks later I still don’t understand what drove this forward motion of the (pp) spot. The runaway had no obvious partner, remaining a unipolar entity. The whole complex passed behind the west limb about July 9 when an M6.9 flare created some fine post flare loop prominences and later a huge surge (earlier reports). The strong activity in the group suggested it might fade away behind the limb – but no, readers, it returned on July 25.

When the (pp) ‘runaway’ left its group the remainder comprised a normal bipolar arrangement, as the runaway was the result of division of the group’s (p) spot with strong-ish 2300G fields. What had happened in the 14 days it spent on the sun’s far-side? To answer this the group was plotted on a synoptic map (Fig) that attempts to clarify the history.

On July 25th two simple spots were seen at the return site (by Mt Wilson, I was clouded out). A check of the old heliocentric positions showed the two AR11515 preceding spots had survived, with the old (p) spot still at its original site, -16,212, and renamed AR11530. And to the west of it was the old (pp) ‘runaway’, now even more removed from its mate at –11, 222. It too has been renumbered as AR11529.

The (Fig) shows it has moved ten degrees of longitude from its static sibling and also moved four degrees closer to the solar equator. The two returning spots are toned grey in the figure – all the other lesser spots have now gone. The figure is much simplified for clarity. The history may be summarised thus:

History: June 30: a complex (p) spot of AR11515 begins to divide. On July 2 it has elongated into an oval with two equal umbrae(Fig,a). By 3 July the oval has split into two well-separated (p) spots (the more western is dubbed pp for clarity, Fig,b1). It, (pp), had huge surges at this time and was moving rapidly westwards relative to the rest of the group, its separation now two degrees.

July 8 saw the complex nearing the west limb with (pp) now 5 or 6 degrees ahead of the group and 3 degrees closer to the equator (Fig,c)!

The return, as related, saw the (pp) spot now ten degrees ahead of the (p) spot but with little change in its latitude (Fig,d). I suspect no more motion in the (pp) spot, but we must wait and see. In an email Bill Livingston describes the pair thus, “They seem to me to be mature objects, that are not going to do much”.

What caused the ‘runaway’? I would still like to know! But thanks to Helio positions we are able to follow these unusual sunspot events, revealing a rare sunspot ‘runaway’.

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