The leftmost image is at the lowest frequency, 0.33 GHz (wavelength of 1 meter), and arises high in the Sun's corona, i.e., the hot atmosphere which lies above the Sun's visible surface. The bright spot to the right is a place high in the atmosphere where electrons are being accelerated to high energies. The Sun looks elongated at this frequency because of the large difference in density of gas between the outer corona above the Sun's poles and the corona at the Sun's equator. Although it doesn't look like it in these thumbnail images, the Sun "looks" bigger at this frequency than it does at the higher frequencies shown in the other images (check the scales in the larger images you see by clicking on the individual frames).