Astronomical Society of Coonabarabran

Late October's Big Prominence (October 2008)

by Harry Roberts

2008 October saw a number of new cycle (C24) sunspot groups and several patches of magnetic field with the distinct reversed polarity that marked them as C24 activity, though no spots emerged there. A large prominence also appeared and became active on the 24th.

2008 has seen many large and at times active prominences, but during October these seemed to be absent - so it was good to see a large faint "hedgerow" at high north latitude in the west on the 23rd 23:00 UT. It was stable at a height of just under 50Mm (50,000km) and stretched around the limb from 44ºN to 51ºN (~80Mm). During steady moments it was seen to consist of numerous short vertical plumes suspended above the sun's surface but connected by foot points at the northern and southern ends. Zirin tells us that any prominence above 50Mm high will erupt within 48 hours - and this example would conform to type.

The next morning Oct 24 23:00 (actually the 25th local date) showed that a tall column structure had replaced the hedgerow. It was situated at 49ºN, longitude 74º, having a base 3º wide and reached a height of more than 100Mm - consisting of two plumes or streams of material (Figs 1 and 2). At steady moments I could see a short filament below the prominence on the disc.

Later observation at 02:30 on the 25th (still local day 25th see Fig 2) showed a much fainter single plume now remained at the site (heliocentric 49ºN, longitude 71º). Next day only a small wisp of suspended prominence was visible at the site - at 52ºN, longitude 59º.

A look back through the log shows that current prominences seem to favour latitudes ±45º, with the majority of them in the north. Monthly synoptic maps are being made in an attempt to detect filaments that are associated with these high latitude prominences, and perhaps pin down any magnetic "hot-spots" on the sun's surface.

Some writers suggest that new cycle activity at first appears at high latitudes, above ±45º, then slowly migrates to lower latitudes where it emerges as sunspots around ±30º - and the current activity of both prominences and new cycle sunspots seems to suggest this process is well under way.

[Ed. A whole disc photograph of the Sun taken on 25 October 2008 by David Samuel can be seen here in the Photo-Gallery section.]

Figure 1

Figure 2