This is how sunlight reaches earth surface

How is the sun shining?

Sun is a massive celestial body that contains tonnes of gas in its core. These gases go under continuous chemical reactions called fusion, an infinite number of particles combining to form a new particle & the process continues.

Why don't we get burnt due to the heat energy of light?

This giant ball of gas is having a diameter of order 10^6 km in comparison to which our teeny-tiny planet's diameter is of order 10^4 km, however, both have separation of around 1.27*10^8 km. Now what we know is that our planet is enveloped by layers of the atmosphere.



These layers are divided on the basis of there particulates. Light has to pass all these layers before reaching the Earth's surface. When anything hits something is produces some impact & the fast-moving object gets slower, the same happens with light. When light enters into the earth's atmosphere it loses its energy to reach the surface. These layers are:-

  • Ionosphere
  • Mesosphere
  • Stratosphere
  • Troposphere
The troposphere contains 99% of the water vapour & 75% of the gases in the atmosphere. Solar radiation is received at the earth's surface in attenuated form because it is subjected to the mechanisms of absorption & scattering, mainly in troposphere & stratosphere. The ozone layer in stratosphere plays an important role in absorbing the harmful UV component of solar radiation. Other wavelengths partially absorbed by water vapour & to a lesser extent by gases.

Beam/Direct Radiation:- Solar radiation received at the earth's surface without change of direction.

Diffused Radiation:- The radiation received at the earth's surface from all parts of the sky's atmosphere.

Global Radiation:- Direct Radiation + Diffused Radiation

AM (Air Mass):- It is defined as the ratio of the atmosphere through which the beam radiation passes to the mass it would pass through if the sun is directly overhead (i.e. at its zenith).

Solar constant was introduced to make the calculations easier, it is the rate at which energy is received from the sun on a unit area perpendicular to the rays of the sun, at the mean distance of the earth from the sun.

The standard value of solar constant was adopted to be 1353W/m^2 in 1971. However, later changed to 1367W/m^2.


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