The sun

THE SUNThe Nearest Star to us

The SunThe governor of Solar System.

Only day time star and closest

star to the Earth.

It is 13,00,000 times bigger

than Earth.

The light takes 8.24 minutes

to reach Earth.

To cover its diameter, 109

Earth will be required.

It emits the radiations in all

Electromagnetic spectrum .

Physical Profile of Sun

Observation data

Mean distancefrom Earth

1.496×108 km

Visual brightness (V) −26.74 

Absolute magnitude 4.85 

Spectral classification G2V

Angular size 31.6′ – 32.7′ 

Physical characteristics

Mean diameter 1.392×106 km

Equatorial radius 6.955×105 km 

Mass 1.9891×1030 kg 

Average density 1.408×103 kg/m3 

Equatorial surface gravity 274.0 m/s2 

Escape velocity 617.7 km/s 

Temperatureof surface (effective)

5,778 K

Luminosity (Lsol) 3.846×1026 

Orbital characteristics

Mean distancefrom Milky Way core

~2.5×1017 km26,000 light-years

Galactic period (2.25–2.50) × 108  yrs

Velocity ~220 km/s(orbit around the center of the Galaxy)

Rotation characteristics

Obliquity 7.25°(to the ecliptic)

Sidereal Rotation period(at 16° latitude)

25.38 days 

(at equator) 25.05 days 

(at poles) 34.3 days 

Rotation velocity(at equator)

7.189×103 km/h 

Atmosphere of Sun

The layer above Photosphere, with the thickness of ~2,000 KM is ‘Chromosphere’.

The outermost layer of the Sun’s atmosphere is known as ‘Corona’, it extends upto millions of kilometer above Chromosphere.

Chromosphere and Corona is visible only during Total Solar Eclipse.

Sun’s atmosphere

starts from and above the

surface layer named

‘Photosphere’.

Photosphere

It is less than 500 KM deep. The photoshpere is the layer in the Sun’s atmosphere that is dense enough to emit plenty of light but not so dense that the light can’t escape.

It is very-low-density gas. The density is 3400 times less dense than the air we breath.

The layer below photosphere is dense and can produce continuous spectra, but atoms in the photosphere absorb photons of specific wavelengths producing absorption lines.

The layer has a mottled appearance because it is made up of dark-edged regions.

It is known as granules and pattern is called as granulation.

Granule lasts for 10 to 20 minutes. Spectra shows that centers are a few hundred degrees hotter than the edges, and Doppler shifts reveals that the centers are rising and the edges are sinking at the speed of 1 km/sec.

ChromosphereChromosphere is 1000 times fainter than the photosphere.

Characteristic flash seen during the total solar eclipse in pink colour is produced in chromosphere – it is a combination of emission lines in red, blue and violet Balmer line.

Chromosphere has low-density gas. It is about 108 times less dense than the air we breath.

At the bottom of layer temperature is low (4300 K) but then rises rapidly. The region where temperature rises rapidly is called transition region.

Corona

Spectrum of corona showed that the temperature is in the order of million degree. It is not bright because it is very low density gas only 1-10 atoms/cm3.

The study showed that the light from outer corona is reflected sunlight i.e. outer corona contains dust particles that reflects sunlight in all directions.

Corona is the region where high speed winds are getting generated known as Solar Wind. It has the velocity of 300-800 km/sec.

Internal Structure of the Sun

COREof the sun

It extends from 0 to 0.25 solar radii.

It has the density of 150g/cm3.It has the temperature of 13.6 to 15 million K.

It is the fastest rotating part.

All of its energy generate in the core through nuclear fusion. 98% is through p-p chain and 2% is through CNO cycle.

Radiative Zone

It starts from 0.25 to 0.70 solar radii.

It is hot and dense which helps in transferring the matter from core to outer

part through radiation.

Material from bottom to top gets cooler with the altitude (7 million to 2 million K).

This is a region where the sharp regime change between the

uniform rotation of the radiative zone and the differential

rotation of the convection zone

Magnetic Activities on the Sun

Solar Flare

A solar flare is a violent explosion

in the Sun's atmosphere with

an energy equivalent to tens

of millions of hydrogen bombs.

Sun Spot

Sunspot is the easily observable magnetic activity on the Sun’s surface.Because of their cooler temperature region at the magnetic region it appears as a dark spot.

The temperature of the sunspot is of the order of 4250K as compared to surrounding of 5700 K.

It has a inside dark part known as umbra and outside lighter part known as penumbra.

The presence of magnetic filed in the sunspot was first observed by Gorge Ellery Hale in 1908 through the Zeeman Effect.

How Aurora forms…

How big is the Sun…

How small is the Sun…

Life Cycle of Sun/Possible end of Sun