Intro About Solar Radiation

8/10/2019 Intro About Solar Radiation

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Lecture Notes No:1Title : The sun and the Earth

The Sun:-

is basically a sphere in shape.

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Contains intensely hot gases matter within it.- It has a diameter of 1.39x109m or 13.9x105 km.-

Distance between the earth and sun is around 1.5x1011m-

It rotates its own axis about 4 weeks.-

Its black body temperature is in the order of 5762 K-

Temperature of the inner core of the sun is estimated between8x106to 40x106K

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Density is 1000 times than the water (Plasma).-

It contains 80% of hydrogen (H2)and 19% of the helium (He).-

Remaining may be 100 plus observed elements makesup the tiny

fraction of this composition of the sun.

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The source of the sun energy may be due to hydrogen to helium inthe thermonuclear fusion reaction.

Anatomy of the sun:

Core:-

90% of thesun energy generated from this region- It distance range is 0 to 0.23 R (where R is the radius of the sun).-

It temperature range is around 8 to 40 x106K.

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Solar wind

Corona

Chromos here

Photos here

Convective shell

Radioactive shell

Core


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Pressure is around 109 atm.-

Its density is around 100 g/cc or 1,00,000 kg/m3.

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It contains 40% of the mass of the sun.-

It occupies around 15% of the volume of the sun.

Radioactive shell:- it is at a distance of 0.7 R from the centre of the sun.-

the temperature across this region is around 1,30,000 K.-

its density drop across this region is around 70 kg/m3.-

After this region, (ie) the outer layer of this region is starts withconvective shell.

Convective Shell:-

it is very important region of the sun.-

The convection process begins from this region.

- It range is 0.7 R to 1R.

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Within this region, the temperature drop is around 5000 K.-

The density drop across this region is about 10-5kg/m3.-

Usually the sunspots are appeared in this region only.-

The outer most layer of this region is photosphere.

Sunspots:-

it is a temporary phenomenon on the photosphere of the sun.- this appears visibly as dark compared to its surrounding areas,-

these are caused by the inverse magnetic activity which inhibitsconvection by an effect comparable to eddy current brake, forming

the area of the reduced surface temperature.-

The temperature of this spot is around 3000 to 4000 K whereas

surrounding temperature is around adiabatic flame temperature isabout 5780 K.

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If the sunspot is isolated from the surrounding materials, it wouldbe brighter than the electric arc.

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It can expands or contracts as they move across the surface of thesun.

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Max sunspot identified appears and viewed from the earth isaround 80,000 km.

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Its relative speed of its travel is few hundred miles per second.

Photopshere:

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The edge of the photosphere is sharply defined.-

It is in the range of 1.015 R.-

The temperature across this region is around 5000 K to 106K.

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It density of the gases in this layer are in the range of 10-8 to 10-4g/cc.

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It is composed of the gases are strongly ionized and able to absorband emit a continuous spectrum of radiation.

- It is the source of the most of the solar radiation.


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The outer most layer of the photosphere is called chromosphere.

Chromosphere:-

it is more or less transparent atmosphere.

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It can be observed during the solar eclipse or by instrumental that

obscure the solar disk.- Above the photosphere, there is layer of cooler gases for several

hundred kilometers deep, called the reversing layer.-

It temperature are in the region is 106K.-

This temperature range prevails upto the layer of corona.-

It density across this layer is very low (10-4 to 10-6 g/cc).-

It distance depth about 10,000 km.-

The outer lost layer of this region is corona.

Corona:- it is of very low density.

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Its temperature is in the high range of about 106K.-

This corona can be seen only during the solar eclipse.

The Earth:-

it shaped as an oblate spheroid. (ie) a sphere flattened at the polesand bulging in the plane normal to the poles.

- It can be assumed as sphere for many practical purposes.-

It diameter is about 12,800 km at the equatorial plane.-

It has circumferential distances at:

Equatorial plane is 40,075.17 km Meridionial plane is 40,007.86 km

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the surface area of the earth is: total area is about 510,072,000 km2

land area is about 148,292,000 km2- 29.2% water area is about 361, 780,000 km270.8%.

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it makes one rotation about its own axis in every 24 hours.-

It completes a revolution around the sun in a period of approx.365.25 days.

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The mean density of the earth is 5.517 g/cm3.-

It has a central core of about 2,560 km in diameter which is more

rigid than steel.-

Beyond this core, there is mantle, which forms about 70% of the

earths mass.-

Beyond this is the outer layer of the earth is so called crust, whichforms about 1% of the earths mass.

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The earth revolves the sun in an elliptic orbit with latter at one ofits foci of the ellipse.

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The apparent path of the sun s seen from the earth is known asecliptic.


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The eccentricity of the earths orbit is such that the distancebetween the sun and earth varies by 1.7%.

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The mean sun-earth distance is 1.495x1011km.

Sun-earth distance:

SUN

1.495 X 1011m 1.7%

1.39x109 m

1.27x107 m

32

EARTH


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Black body Radiation:

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The energy density of the radiation emitted at a given wave length(monochromatic) by a perfect radiations, usually called a black

body.

- 25)T/C(

1

bn)1e(

CE2

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Where, Eb= Monochromotaic emissive power of the black

body. C1= 3.74 x 108 W. m4/m2

C2= 1.44 x 104 m K n = Refractive index of the medium

For vacuum n=1:For air taken to be n=1.

- Monochromotic emissive power means energy emitted by a perfect

radiator per unit wave length at the specified wave length per unit areaper unit time at the temperature T.

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Now, the total energy emitted by the black body is integrating theabove equation over wavelengths,

dEE

0

bb

Where,Eb= total emissive power of the black body in W/m2

The total Energy emitted by the sun from its outer surface is given by,

4

ssb T*A**E

Where, = Stefan Boltzmanns constant = 5.67x10-8W/m2K4

T = Suns outer surface absolute temperature in K. = Emissivity of the sun

A = Surface Area of the sun in m2

Why do we need the solar energy?

Ans:-

is the worlds most abundant permanent source of the energy.


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Amount of this energy intercepted by the earth is about 5,000times greater than the sum of the other forms of energy sources

(like nuclear, geothermal, gravitational energies, lunar gravitationalenergy etc.,)

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Out of this energy intercepted,

30% of the energy is reflected back to space. 47% is converted to low temperature heat and again

reradiated back to space. 23% is used for evaporation and precipitation of

biosphere.

Less than 0.5% is represented in the KE of the windand waves

Remaining amount are stored in the forms ofphotosynthesis in plants.

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The total terrestrial radiation is only about one third of the

extraterrestrial radiation total during a year.

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70% of the energy falls on the ocean-

Only 1.5x1017kW hr falls on the land == Which is equal to 6,000 times the total energy usageof USA IN 2000.

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Intro About Solar Radiation