The Sun is the closest star to Earth and governs the Solar System. It is about 13,00,000 times bigger than Earth and composed of a dense core, radiative zone, and convective zone. Its atmosphere consists of the photosphere, chromosphere, and corona. Nuclear fusion in the core powers the Sun, primarily through the proton-proton chain. Magnetic activity on the Sun includes sunspots and solar flares. The Sun will eventually exhaust its nuclear fuel and expand into a red giant star before shrinking into a white dwarf over its lifetime of approximately 10 billion years.

1. THE SUN
The Nearest Star to us

2. The Sun
The 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 .

3. Physical Profile of Sun
Observation data
Mean distance
from 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
Temperature
of surface (effective)
5,778 K
Luminosity (Lsol) 3.846×1026
Orbital characteristics
Mean distance
from Milky Way core
~2.5×1017 km
26,000 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

4. Atmosphere of Sun
Sun’s
atmosphere
starts from and
above the
surface layer
named
‘Photosphere’.
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.

5. 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.

6. 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.

7. Chromosphere
Chromosphere 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.

8. 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.

9. Internal Structure of the Sun

10. CORE
of 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.

11. Radiative Zone
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
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).

12. 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.

13. 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.

14. How Aurora forms…

15. How big is the Sun…

16. How small is the Sun…

17. Life Cycle of Sun/Possible end of Sun