in traditional Chinese astronomy for those Chinese constellations that surround the north celestial pole. Geography Purple Mountain is located on the eastern side of Nanjing. Its peaks are often found enveloped in purple clouds at dawn and dusk, hence comes its name "Purple Mountain". The Purple Mountain Observatory is located there. Purple Mountain in County Kerry, Ireland, takes its name from the color of the shivered slate on its summit. Purple Mountain in Wyoming (el. ) is a mountain peak in the southern section of the Gallatin Range in Yellowstone National Park. Purple Mountain, Alaska Purple Mountain, Oregon Purple Mountain, Washington Purple Peak, Colorado Purple mountains phenomenon It has been observed that the greater the distance between a viewers eyes and mountains, the lighter and more blue or purple they will appear. This phenomenon, long recognized by Leonardo da Vinci and other painters, is called aerial perspective or atmospheric perspective. The more distant the mountains are, the less contrast the eye sees between the mountains and the sky. The bluish color is caused by an optical effect called Rayleigh scattering. The sunlit sky is blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long wavelength red light. The result is that the human eye perceives blue when looking toward parts of the sky other than the sun. At sunrise and sunset, the light is passing through the atmosphere at a lower angle, and traveling a greater distance through a larger volume of air. Much of the green and blue is scattered away, and more red light comes to the eye, creating the colors of the sunrise and sunset and making the mountains look purple. The phenomenon is referenced in the song "America the Beautiful", where the lyrics refer to "purple mountains' majesty" among other features of the United States landscape. A Crayola crayon called Purple Mountain Majesty in reference to the lyric was first formulated in 1993. Mythology Julius Pollux, a Greek grammarian who lived in the second century AD, attributed the discovery of purple to the Phoenician god and guardian of the city of Tyre, Heracles. According to his account, while walking along the shore with the nymph Tyrus, the god's dog bit into a murex shell, causing his mouth to turn purple. The nymph subsequently