THE COLOURS OF THE SKIES

The colours of the sky depends on the position of the sun
and atmosphere.We take the blueness of our sky for granted.But the
skies of other planets in our solar system can be of any
colour.Why? It all depends on the atmospheric density of a
planet,and the gases comprise that atmosphere.Sunlight, which appears white is infact composed of every colour of the spectrum-violet,indigo,blue,green,yellow,orange,red.
And each colour has a different wavelength.Violet and blue
have the shortest wavelengths,orange and red the
longest.Wavelength can be as short as a hundred millionth of
an inch,the size of a simple molecule. The closer the colour wavelength is to the size of a gas
molecule the more it will be bounced around,or scattered,by a
given atmosphere so long as the gas particles themselves do
not absorb sunlight. Our air is a mixer of nitrogen and oxygen.Their particles
are not light absorbent and are as small as the short
wavelengths of blue.Therefore,during the day,the blue light is
more efficiently scattered by the air and we see the sky as
blue.When seen from space the earth appears as a band of blue
at the horizon. Skies of other planets,for example Mars,Venus,Jupiter and
Uranus have different hues. Why is the Mars sky red?Images sent back from the
Viking Mars landers in 1977 and from Pathfinder in 1997 showed
a red sky seen from the Martian surface. This was due to red
iron-rich dusts thrown up in the dust storms occurring from
time to time on Mars. The colour of the Mars sky will change
according to weather conditions. It should be blue when there
have been no recent storms, but it will be darker than the
earth's daytime sky because of Mars' thinner atmosphere. Venus's atmosphere is made up of carbon dioxide and
sulfur.It is so thick that it scatters colour of all but the
longest wavelengths,with sulfur adding a yellowish hue.The
venusian sky is thus seen as a reddish orange. Jupiter's gaint atmosphere is so dense that no light can
pass through to the surface.but in its upper
atmosphere,composed of ammonia ice particles,the sky is
blue-black and still farther down the sky appears red-brown. Uranus's atmosphere is rich in methane and composed of
hydrogen and helium.Methane absorbs the yellow and red light
letting the green and blue filter through.Hydrocarbons remove
some of the blue,so the skies of Uranus are blue-green.