October 02, 2008
In the photo above we’re observing the rising of the Sun, which resembles a drop of amber, over the Atlantic Ocean. The disk of the Sun isn’t yet fully above the horizon, its grazing reflection is immediately below it. At the horizon, sunlight shines through almost 40 times as much air as it does when it’s directly overhead. The deep yellow color of the Sun is due to the greater scattering of the shorter wavelengths of blue and violet sunlight. These colors are effectively removed from our sight, leaving only the longer wavelength yellow and reds to reach our eyes. Note that the top of the Sun appears somewhat lighter because we're looking through less air than when looking at the horizon and thus there’s less short-wave scattering. The Earth's atmosphere is also a refracting medium. Refraction at the horizon lofts the Sun upward by a half a degree -- a full solar diameter. If there was no atmosphere, the Sun would still be below the horizon. Because of refraction, however, the Sun’s lower limb is raised upward more than the upper limb, resulting in its oval shape, which disappears as the Sun climbs higher in the sky. Photo taken on March 22, 2008 from Jekyll Island, Georgia.