planet's climate is decided by its mass, its distance from the sun and the
composition of its atmosphere. Mars is too small to keep a thick atmosphere. Its
atmosphere consists mainly of carbon dioxide, but the atmosphere is very thin.
The atmosphere of the Earth is a hundred times thicker. Most of Mars' carbon
dioxide is frozen in the ground. Mars' average surface temperature is about
-50°C. Venus has almost the same mass as Earth but a thicker atmosphere,
composed of 96% carbon dioxide. The surface temperature on Venus is +460°C.
Earth's atmosphere is 78% nitrogen, 21% oxygen, and 1% other gases. Carbon
dioxide accounts for just 0.03 - 0.04%. Water vapour, varying in amount from 0
to 2%, carbon dioxide and some other minor gases present in the atmosphere
absorb some of the thermal radiation leaving the surface and emit radiation from
much higher and colder levels out to space. These radiatively active gases are
known as greenhouse gases because they act as a partial blanket for the thermal
radiation from the surface and enable it to be substantially warmer than it
would otherwise be, analogous to the effect of a greenhouse. This blanketing is
known as the natural greenhous effect. Without the greenhouse gases, Earth's
average temperature would be roughly -20°C. The climates on Mars and Venus are
very different, but very stable and highly predictable. The Earth's climate is
unstable and rather unpredictable as compared with that of the other two
The atmosphere is divided into five
layers. It is thickest near the surface and thins out with height until it
eventually merges with space.
1) The troposphere is the
first layer above the surface and contains half of the Earth's atmosphere.
Weather occurs in this layer.
2) Many jet aircrafts fly in the stratosphere
because it is very stable. Also, the ozone layer absorbs harmful rays from the
3) Meteors or rock fragments burn up
in the mesosphere.
4) The thermosphere is a
layer with auroras. It is also where the space shuttle orbits.
5) The atmosphere merges into space
in the extremely thin exosphere. This is the upper limit of our
Weather Service Graphic
inhabitants of our planet live in the Troposphere.
atmosphere varies in density and composition as the altitude increases
above the surface. The lowest part of the atmosphere is called the
troposphere (and it extends from the surface up to about 10 km (6 miles).
The gases in this region are predominantly molecular Oxygen
) and molecular Nitrogen (
). All weather is confined to this lower region and it contains 90% of the
Earth's atmosphere and 99% of the water vapor. The highest mountains are
still within the troposphere and all of our normal day-to-day activities
occur here. The high altitude jet stream is found near the tropopause at
the upper end of this region.
layer above this is the Stratosphere, this is where the Ozone Layer is
formed. The atmosphere above 10 km is called the stratosphere. The gas is
still dense enough that hot air balloons can ascend to altitudes of 15 -
20 km and Helium balloons to nearly 35 km, but the air thins rapidly and
the gas composition changes slightly as the altitude increases. Within the
stratosphere, incoming solar radiation at wavelengths below 240 nm. is
able to break up (or dissociate) molecular Oxygen (
) into individual Oxygen atoms, each of which, in turn, may combine with
an Oxygen molecule (
), to form ozone, a molecule of Oxygen consisting of three Oxygen atoms (
). This gas reaches a peak density of a few parts per million at an
altitude of about 25 km (16 miles).
Ozone Layer absorbs ultra-violet radiation from the Sun. Without the Ozone
Layer life as we know would cease to exist on our planet. Ozone is
important because it is the only atmospheric gas which absorbs light in
the B region of UVB rays.
Ozone layer extends from a height of 20 kilometers to 60 kilometers above
the Earth's surface. The air is very thin at these altitudes.
all of the Ozone in the Earth's atmosphere were compressed into a single
layer at the Earth's surface, it would only be 3 millimeters
thick-basically two stacked pennies!
gas becomes increasingly rarefied at higher altitudes. At heights of 80 km
(50 miles), the gas is so thin that free electrons can exist for short
periods of time before they are captured by a nearby positive ion. The
existence of charged particles at this altitude and above, signals the
beginning of the ionosphere a region having the properties of a gas and of
Hole increases in size during the months of September and October
temperature profile through the lower layers of the atmosphere. Height (in
miles and kilometers) is indicated along each side. Temperatures in the
thermosphere continue to climb, reaching as high as 2000°C.
National Weather Service
The troposphere begins at the Earth's
surface and extends up to 4-12 miles (6-20 km) high. This is where we live.
As the gases in this layer decrease with height, the air become thinner.
Therefore, the temperature in the troposphere also decreases with height. As
you climb higher, the temperature drops from about 62°F (17°C) to -60°F
(-51°C). Almost all weather occurs in this region.
The height of the troposphere varies from the equator to the poles. At the
equator it is around 11-12 miles (18-20 km) high, at 50°N and 50°S, 5 1/2 miles
and at the poles just under four miles high. The transition boundary
between the troposphere and the layer above is called the tropopause. Both
the tropopause and the troposphere are known as the lower atmosphere.
The Stratosphere extends from the
tropopause up to 31 miles above the Earth's surface. This layer holds 19
percent of the atmosphere's gases and but very little water vapor.
Temperature increases with height as radiation is increasingly absorbed by
oxygen molecules which leads to the formation of Ozone. The temperature
rises from an average -76°F (-60°C) at tropopause to a maximum of about 5°F
(-15°C) at the stratopause due to this absorption of ultraviolet radiation.
The increasing temperature also makes it a calm layer with movements of the
The regions of the stratosphere and the mesosphere, along with the
stratopause and mesopause, are called the middle atmosphere by scientists.
The transition boundary which separates the stratosphere from the mesosphere
is called the stratopause.
The mesosphere extends from the
stratopause to about 53 miles (85 km) above the earth. The gases, including
the oxygen molecules, continue to become thinner and thinner with height. As
such, the effect of the warming by ultraviolet radiation also becomes less
and less leading to a decrease in temperature with height. On average,
temperature decreases from about 5°F (-15°C) to as low as -184°F (-120°C)
at the mesopause. However, the gases in the mesosphere are thick enough to
slow down meteorites hurtling into the atmosphere, where they burn up,
leaving fiery trails in the night sky.
The Thermosphere extends from the
mesopause to 430 miles (690 km) above the earth. This layer is known as the
The gases of the thermosphere are increasingly thinner than in the
mesosphere. As such, only the higher energy ultraviolet and x-ray radiation
from the sun is absorbed. But because of this absorption, the temperature
increases with height and can reach as high as 3,600°F (2000°C) near the
top of this layer.
However, despite the high temperature, this layer of the atmosphere would
still feel very cold to our skin because of the extremely thin air. The
total amount of energy from the very few molecules in this layer is not
sufficient enough to heat our skin.
The Exosphere is the outermost layer of
the atmosphere and extends from the thermopause to 6200 miles (10,000 km)
above the earth. In this layer, atoms and molecules escape into space and
satellites orbit the earth. The transition boundary which separates the
exosphere from the thermosphere below it is called the thermopause.
source: US Department of
The amount of carbon dioxide in the atmosphere has
been increasing rapidly. Human
activities are also releasing other "greenhouse"
gases such as methane, ozone, and chlorofluorocarbons (CFCs), which intensify the
heat-trapping properties of the atmosphere as a whole.
will continue to grow and contribute to Global Warming
CFCs also rise into the upper
layer of the atmosphere, the stratosphere, where they destroy the protective
layer of ozone, a gas that forms a shield against ultraviolet rays that can harm many
forms of life.
NASA TOMS Ozone Hole image
About l million tons (over 900,000
metric tons) per year of CFCs have been released worldwide since the mid-l970s.
factories have no pollution controls in developing nations
Concern is growing that atmospheric changes could bring
on rapid, profound climatic changes.
Atmospheric concentrations of greenhouse gases are
rising at unprecedented rates. Greenhouse gas emissions from developing countries
are expected to increase rapidly. Large-scale climate changes may occur unless
other climatic systems counteract the warming effect of the greenhouse gases.
Total global energy use is projected to grow at an annual
rate of 1.5-2 percent. Non-fossil energy sources are likely to become more
important because of concern over global warming.
Cleaner, more efficient energy technologies can
significantly reduce greenhouse gases from fossil fuels, especially over
the next 20 years. However, total greenhouse gas emissions are likely to
increase due to expanded energy use.
kills more people than car
Demand for refrigeration (which
has cooling systems that use CFCs) in developing countries is projected to
increase greatly, especially in China and India.
Ozone losses in the upper atmosphere
are occurring at all latitudes in both hemispheres. The most striking example
of ozone loss occurs over the South Pole during September and October. As
ozone is lost, the amount of biologically harmful UV-B radiation will increase.
Skin cancer rates are expected to increase. Other health effects will likely
include an increase in cataracts and suppression of the immune system. Increased
UV-B radiation may also harm plants and animals.
Why is the Sky Blue?
It is easy to see that the sky is
blue. The light from the Sun looks white. But it is really made up of all
the colors of the rainbow.
A prism is a specially shaped
crystal. When white light shines through a prism, the light is separated into
all its colors.
Wavelength in microns
Like energy passing through the
ocean, light energy travels in waves, too. Some light travels in short,
"choppy" waves. Other light travels in long, lazy waves. Blue light
waves are shorter than red
All light travels in a straight line
unless something gets in the way to--
reflect it (like a mirror)
bend it (like a prism)
or scatter it (like molecules of
the gases in the atmosphere)
Sunlight reaches Earth's atmosphere and is
scattered in all directions by all the gases and particles in the air. Blue
light is scattered in all directions by the tiny molecules of air in Earth's
atmosphere. Blue is scattered more than other colors because it travels as
shorter, smaller waves. This is why we see a blue sky most of the time.
Closer to the horizon, the sky fades
to a lighter blue or white. The sunlight reaching us from low in the sky has
passed through even more air than the sunlight reaching us from overhead. As the
sunlight has passed through all this air, the air molecules have scattered and
rescattered the blue light many times in many directions. Also, the surface of
Earth has reflected and scattered the light. All this scattering mixes the
colors together again so we see more white and less blue.
Why do we see rainbows in the
A rainbow is an optical and
meteorological phenomenon that causes a spectrum of light to appear in the sky
when the Sun shines onto droplets of moisture in the Earth's atmosphere. They
take the form of a multi-colored arc, with red on the outer part of the arch and
violet on the inner section of the arch. A rainbow spans a continuous spectrum
of colors. Traditionally, however, the sequence is quantised. The most commonly
cited and remembered sequence, in English, is Newton's sevenfold in order from
longest to shortest wavelength: red, orange, yellow, green, blue, indigo and
"Roy G. Biv" and "Richard Of York Gave Battle In
Vain" are popular mnemonics. Rainbows can be caused by other forms of water
than rain, including mist, spray, and dew.
Sunlight contains many different
colors. Normally, we see all the colors mixed together as white light. We see a
rainbow when sunlight separates into bands of different colors. These bands of
red, orange, yellow, green, blue, indigo, and violet light are also known as the
A rainbow is created when sunlight
passes through raindrops. Light travels through different substances at
different speeds. When light travels through water, it slows down. The reduced
speed causes light to bend or refract.
To understand how a rainbow is made,
it is helpful to understand how a prism works. A prism is a triangular shaped
piece of glass. The path of a light beam changes as it goes through a prism.
Glass slows the speed of light. When light travels through a prism, it is
refracted once while going in and again as it passes through. The refraction
separates white light into its many colors.
A water drop acts like a
prism. Light refracts as it enters and leaves a drop of water. The refracting
light is separated into the colors of the spectrum. When the sky is filled with
drops of water, a rainbow is created. Light that enters the drops is refracted.
Refraction makes each color visible in its own band. Each color of the spectrum
has a slightly different wavelength. The different wavelengths bend in slightly
different ways. Long wavelengths bend the least, while short wavelengths refract
the most. Red light has the longest wavelength and violet light has the
shortest. The other colors have wavelengths that fall between. Because color
refraction is consistent, the colors of the rainbow or any other spectrum look
the same and appear in the same order. We use the memory device ROYGBV (Roy G.
Biv) to signify the order of colors.
The combination of all the separated
colors creates the beautiful arching rainbow. Since light needs to pass through
the raindrops, rainbows are always seen in the part of the sky opposite the Sun.
We see the colors of a typical rainbow as light comes from our Sun. Any star
similar to our Sun would create a rainbow with the same colors. Light from
different types of stars would create different colored rainbows, some that we
couldn't even see with our eyes. Astronomers study how a star's light separates.
This separation is called the star's spectrum.
Some Interesting Facts about
When you see a
after rain. The sun is always behind you and the rain in front of you
when a rainbow appears, so the center of the rainbow's arc is directly
opposite the sun.
Most people think...
colors of a rainbow are red, orange, yellow, green, blue, indigo, and
violet, but a rainbow is actually made up of an entire continuum of
colors - even colors the eye can't see!
We are able to see the
colors of a rainbow because...
different colors is refracted when it travels from one medium, such as
air, and into another- -in this case, the water of the raindrops. When
all the colors that make up sunlight are combined, they look white,
but once they are refracted, the colors break up into the ones we see
in a rainbow.
own "personal" rainbow. When you look at one, you are seeing
the light bounced off of certain raindrops, but when the person
standing next to you looks at the same rainbow, they may see the light
reflecting off other raindrops from a completely different angle. In
addition, everyone sees colors differently according to light and how
their eyes interpret it.
You can never...
reach the end of a rainbow, where a pot of gold supposedly awaits. As
you move, the rainbow that your eyes see moves as well, because the
raindrops are at different spots in the atmosphere. The rainbow, then,
will always "move away" at the same rate that you are
credits: NOAA, NASA, EPA, National
Weather Service, Cambridge University, U.S. Navy, The Franklin institute, UK MET