Four stages in the sunset of 23 April 1995, photographed by Dr. Andrew T. Young from Torrey Pines, north of La Jolla, Calif.:
a) (upper left) 7:21:10 p.m.(Pacific Daylight Time) Early stage in the sunset, showing the normal extinction gradient (lower part of Sun is darker and redder). The indentations about 1/3 of the way up from the bottom of the disk indicate temperature inversions. True sun altitude = +40'.
b) (upper right) 7:24:15 p.m.(PDT) This stage shows a reversed extinction gradient: the widest part of the image is brighter and yellower in color than the upper part. The sudden decrease in width below the wide yellow strip shows that we are looking down through an inversion layer and out the other side. The flattened bottom of the image is not the horizon, but is due to strong refractive compression of the lower limb. True sun altitude = +2'.
c) (lower left) 7:26:09 p.m.(PDT) Three separate images are visible. The upper one is the brightest, and yellow in color. The bottom image, which appeared in the dark space below the image in part (b), is dimmer and redder, indicating that it is seen through a longer aerosol path. The middle image, just appearing between the others at this stage, is still redder and darker; it has passed through the most aerosol. The equal widths of the top and bottom images indicate that they are nearly complete, but highly compressed, images of the Sun. The horizon is at the lower edge of the bottom (rectangular) image. True sun altitude = -20'.
d) (lower right) 7:26:50 p.m.(PDT) The middle image has expanded to join the top and bottom images of (c). The disappearance of the dark strips in (c) is characteristic of looking down through an inversion. Note the serrated edges of the image, which indicate a complex series of thermal inversions in addition to the main ones. All three images now show the full width of the Sun. True sun altitude = -29'.