The picture below shows an image of the Sun at a wavelength of 3 mm, observed with the NRAO 12 Meter Telescope at Kitt Peak, AZ on July 11 1991. A solar prominence is visible on the west (right) limb of the Sun, relatively cool (6000 K), dense (10^10/cc) gas suspended some 50,000 km above the photosphere. The following day, this prominence had disappeared. The structure within the solar disk is much more stable, and apart from the solar rotation was largely unchanged the following day.