SUN PILLARS are formed when sunlight reflect from ice crystal cirrus
clouds. Long, slender, prismatic rods of ice align themselves in the
atmosphere and provide a multitude of tiny reflecting surfaces. This
picture is taken just after sunset over the White Tank Mountains just west of
Phoenix, Arizona. It is typical for sun pillars to be observed before
sunrise or after sunset.
SKY COLOR is influenced primarily by impurities like dust or smoke.
Normally the sky is blue as sunlight is scattered by atmospheric nitrogen.
In this photo the night sky is approaching the western horizon and changing the
blue sky to black. Notice that near the horizon the sky is still lightly
colored yellow to yellowish orange as the last rays of sunlight make their way
to the Earth's surface.
RED SUNSETS are created when there is an abundance of impurities in our
atmosphere. As sunlight passes through the thick layer of air at sunset,
the shorter wavelength portions of sunlight are absorbed or scattered
away. This leaves the longer, more penetrating longer wavelength to pass
through the atmosphere - these are the red, orange and yellow wavelengths.
Even higher quantities of dust or smoke will eliminate the yellow and orange
leaving only the red to pass through. The very red sunset over Lake
Ontario attests to the high amounts of particulates in the atmosphere.
RED SKY This is the result of a volcanic eruption. El Chicon of
south central Mexico erupted and inundated the upper atmosphere with sulfur
dioxide. This gas absorbed water from the atmosphere to produce sulfuric
acid droplets. This greatly reduced the amount of sunlight penetrating the
atmosphere and created very red sunset for an entire summer. The streaks
across the sky are stars and the largest streak interrupted by white dots is the
path of an airplane as it flew past during the long photographic exposure.
This photo was obtained just north of Phoenix, Arizona.
Cirrus clouds at sunset.
Cirrus clouds at sunrise.
