Seeing-impaired Folk and an Elephant

Science Nugget: August 20, 1999

1. Introduction

This science nugget will be brief, because there's little time! The point of the title is that we began observations this week of an eruptive solar active region of the "sigmoid" conformation. It appeared in such different guises to SOHO, Yohkoh, and to Big Bear Solar Observatory that at first it seemed as though we were inspired by entirely different phenomena! As readers of these nuggets will know, the visibility of large bright S-shaped (or anti-S-shaped, preferentially in the northern hemisphere) X-ray structures is a predictor of eruptions. This week we've launched a Max Millenium campaign based on that premise.

2. What we saw

The movies below show some of the motions that we caught in a flare of August 17, which was one of those leading to the choice of this region for a major international observing effort.

Here notice please ejection and streaming apparently along the magnetic field lines of the large flare loops. These are one of the "elbows" of the sigmoid.

Here note the funny wisp-like brightenings resulting from the filament eruption, in the apparently quiet corona to the N of the sigmoid.

3. What's happening

Alas, as the campaign proceeds, two unfortunate things have happened. First, the active region on the SE limb became very bright (note the sun has rotated a lot between the time covered by the movies and the time of this whole-Sun image):  This meant that SXT could not freely observe the sigmoid (for technical reasons; we would overexpose too deeply). Second, the sigmoid itself became faint (but still beautifully sigmoidal) and has not cooperated very well with eruptions. This confirms what we already knew too well, namely that we haven't completely figured the Sun out yet! But if we weren't continually surprised and amazed, research would not be so interesting, nor probably so fruitful. Please check next week for the rest of the story.

H. Hudson (

August 20, 1999