Friday, 31 August 2012

AR11520: Ghost that Walks!

An impressive prominence at the sun's SE limb on 2012 August 27 suggested a large filament was about to appear. Next day it was very distinct on the disc at the foot of the prominence.  On the 30th it was wholly on the disc - an impressive sight - flanked by tiny spot groups11562 and 563. 'Helio' sited the filament, apparently, right on the old AR11520 site from early July (posts below). Big active region filaments like this can erupt spectacularly.  And it did so as I slept: on Aug 31 22:00 UT an array of bright flare ribbons were strewn across the site (a-a and b-b), as well as a few filaments that had somehow survived the ejection's turmoil. GOES logged a long-lived C8.4 flare at the site with a beautiful flare arcade in SDO AIA EUV images. The old AR11520 site is far from dead yet!

And readers, last night my friends at ASNSW saw fit to grant me the McNiven Award for astronomy : a very proud moment indeed.

Friday, 3 August 2012

Post flare loops in AR11520

So AR 11520 has not returned after its second transit of the solar far-side. This 'rough' sketch of coronal loops above the AR11520 site on July 18 (as it passes behind the limb) is posted to show some of the southern giant's more extreme behaviour. I will eventually redraw it for presentation. The physics of the loops formation is discussed in earlier posts - they are one of the most beautiful sights anywhere - and notoriously hard to photograph. Webcam users have the best chance as the bright loops saturate in most photos. The human eye almost never saturates, and can see the thin brilliant loops - and follow the tiny bright droplets of condensate (~3000km dia) as they slide down the loops to the flare ribbon sites. The ribbons were no longer visible to me, the M1.7 flare was eight hours earlier. These loops were growing faint - but superb nonetheless. The tall straight ones may be edge-on loops or surges caught up in the event. The grid lines are 20,000Km apart and the loops are a little above 100,000km (100Mm) high.