File:Hxr motion.png

TRACE 171 Å image prior to a GOES C8.9 flare, overlaid with centroid positions of the hard X-ray (HXR) looptop emission (in a '+' symbol) and of the HXR footpoints (in a 'x' symbol), observed by RHESSI during the flare. The time evolution of the centroid positions is color-coded, and the positions are differentially rotated to 2005 July 30 16:40:34 UT, the time when the TRACE image was taken. A collection of coronal loops, which first contracted, then expanded, and erupted during the flare, is labeled 'L'. A filament appearing in absorption is labeled 'F', which erupted with the coronal loops during their expansion phase. A horizontal slit is placed across the group of coronal loops to study their contraction.