Exosphere and Karman Line

• Exosphere is the outermost layer of the atmosphere, extending from the top of the thermosphere to 10,000 km above the earth.
• The air in the exosphere is extremely rarefied, and the temperature gradually increases through the layer.
• The exosphere gradually merges with the outer space.
• In the exosphere layer, atoms and molecules escape into space, and satellites orbit the earth.
• At the bottom of the exosphere is the thermopause, located around 600 km above the earth.

Karman Line

• The Karman Line is the internationally recognized boundary of space.
• The Federation Aeronautique Internationale (FAI) defines the Karman Line as the altitude of 100 kilometers (62 miles) above Earth's mean sea level.
• The Karman Line is the line where atmospheric lift no longer supports a flying object and the object would need to reach orbital velocity.
• FAI is the world governing body for air sports and also stewards definitions regarding human spaceflight.
• Other organizations such as NASA and US Air Force do not use this definition of the Karman Line.
• There is no international law defining the edge of the space and therefore the limit of national airspace.

Concept of Twilight

• Twilight is the period of diffused light in the sky that occurs before and after sunset, when the sun is below the horizon but its rays scatter through Earth's atmosphere.
• Twilight is caused by the scattering of sunlight by the atmosphere, illuminating the sky in varying degrees of brightness.

Mesosphere

• The mesosphere lies above the stratosphere and extends up to a height of 80 km.
• In the mesosphere layer, temperature again starts decreasing with the increase in altitude.
• The upper limit of mesosphere is known as the mesopause.
• Polar mesospheric noctilucent clouds are the highest clouds in the atmosphere, which are visible to naked eyes.
• Meteors fall and burn in the mesosphere.

Thermosphere

• The thermosphere is between about 85 km and 600 km.
• This layer is known as the upper atmosphere.
• This layer contains electrically charged particles known as ions and therefore, ionosphere is a part of this layer.
• The ionosphere layer is helpful in reflecting the radio waves transmitted by the Earth and helps in telecommunication.
• The thermosphere layer reflects an increase of temperature with height because of the absorption of incoming high-energy ultraviolet and x-ray radiation from the sun by the molecules in this layer.
• The International Space Station (ISS) and satellites orbit in the thermosphere layer.
• Auroras are observed in the lower parts of this layer.

Auroras

• An aurora is a natural light display in the sky, predominantly seen in high latitudes (Arctic and Antarctic) regions.
• Auroras are known as Aurora Borealis when they occur in the North Pole and as Aurora Australis when they occur in the South Pole.
• Auroras are caused by the interaction of charged particles from the sun with the Earth's magnetic field and atmosphere.
• The collisions of these particles with the atmosphere release energy in the form of light.
• The colors observed in auroras depend on the type of gas and altitude of the collision.

Troposphere

• Its height also changes from one season to another.
• The temperature in the troposphere layer decreases which is called normal lapse rate.
• The zone separating the troposphere from the stratosphere is known as tropopause and thus represent a zone of constant temperature.
• All changes in the climate and weather take place in this layer (e.g. fog, cloud, dew, frost, rainfall, storms, thunder, etc.).
• The troposphere is the most important layer for all biological activity.
• This layer contains all dust particles and water vapor.

Stratosphere

• The stratosphere is found above the tropopause and extends up to a height of 50 km.
• Contains the ozone layer which absorbs the ultraviolet radiations and shields life on the Earth from intense harmful forms of energy.
• Temperature in the stratosphere remains constant for some distance but then starts rising due to the presence of ozone.
• Though the stratosphere is more or less free from clouds and devoid of major weather phenomena, making conditions most ideal for flying airplanes.
• Sometimes, there is circulation of feeble winds and presence of Cirrus clouds in the lower stratosphere.
• The air in the stratosphere is very dry and it is about a thousand times thinner here than it is at sea level.
• The stratosphere is where jet aircrafts and weather balloons fly.