The Sun
(Nearest Star to us)
Dr. Arvind C. Ranade
Flow of Talk
Our SUN
 Physical Profile of Sun
 Sun among other Stars
 Atmosphere of Sun
 Photosphere
 Chromosphere
 Corona
 Internal Structure of Sun
 Core
 Radiative Zone
 Convective Zone
 Magnetic Activities on Sun
 Sunspot Cycle/Magnetic Cycle
 Effect on the Earth
 Possible end of Sun
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Our 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 (Gamma Rays to
Radio waves).

Physical Profile of Sun
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
5,778 K
Luminosity (Lsol)
3.846×1026
of surface (effective)
Rotation characteristics
Obliquity
7.25°
Sidereal Rotation period
25.38 days
(at equator)
25.05 days
(at poles)
34.3 days
Rotation velocity
7.189×103 km/h
(to the ecliptic)
(at 16° latitude)
(at equator)
Observation data
Orbital characteristics
Mean distance
~2.5×1017 km
Galactic period
(2.25–2.50) × 108
Velocity
~220 km/s
from Milky Way core
Mean distance
1.496×108 km
Visual brightness (V)
−26.74
Absolute magnitude
4.85
Spectral classification
G2V
Angular size
31.6′ – 32.7′
from Earth
26,000 light-years
yrs
(orbit around the center of the
Galaxy)
Sun among other Stars
Spectral Class (Temp)
O – > 30,000 K
B - 30,000- 12,000 K
A – 12,000- 9,000 K
F – 9,000 – 7,000 K
G – 7,000- 5,500 K
K – 5,500 – 3,800 K
M - < 3,800 K
 Luminosity Class
(Spectral lines)
I – Super giants
II-III – Giant
IV-V - Dwarf

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.
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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.
Photosphere
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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.
Chromosphere
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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
lowdensity 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.
Chromosphere
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An H-alpha filtergram reveals that the chromosphere
contain complex structure which is invisible in normal
photographs.
Spicules are characteristic flamelike jets of gas, rise
upward into the chromosphere and last for 5 to 15
minutes.
Corona
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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.
The “invisible” corona is seen only when the bright photosphere is masked by moon
during total solar eclipse. Alternatively, from space by artificial eclipse, and in xray, UV lights.
Temperature profile of the
Sun’s atmosphere
Opacity on the Sun’s atmosphere
corona
density
temperature
Temperature
and
Density
over
the outer
solar
atmospheric
layers
chromosphere
photosphere
Internal Structure of the Sun
• Helioseismology gives the answers to the internal structure of Sun.
• Global Oscillation Network Group (GONG)
Core
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.
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P-P Chain
• In the core of Sun, proton-proton
chain occurs 1037 times in each second.
• The Sun exhausts 4.26 million metric
tons of matter in every second.
383 yottawatts (3.83×1026 W).
C-N-O Chain
In
the
CNO
cycle,
four protons fuse, using carbon,
nitrogen and oxygen isotopes as a
catalyst, to produce one alpha
particle, two positrons and two
electron neutrinos. The positrons
will
almost
instantly annihilate with
electrons, releasing energy in the
form of gamma rays.
Radiative Zone
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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).
Density drops to hundred folds
(20 g/cm3 to 0.2 g/cm3).
Region of random walk problem.
The region between the radiative
zone and the convection zone is a
transition
layer
called
the tacholine.
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.
Convective Zone
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It is the outer layer in the
internal structure and it starts
from below photosphere down
to about 200,000 km.
The solar plasma is not dense
enough or hot enough to
transfer the heat energy of the
interior outward via radiation.
Thermal convection is the
process through which thermal
columns carry hot material to
the surface (photosphere) of
the Sun.
It is the region where granules
and supergranules originates.
The turbulent convection in the
outer part gives rise to the
small
scale
dynamo
which
produces magnetic south and
north.
Magnetic Activities on the Sun
Solar Flares
Sunspots
Prominences
Sunspot Cycle/Magnetic Cycle
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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.
Sunspots
Zeeman
Effect
• Size of the sunspot varies from 1000 km to 80,000 km.
• Life of Sunspot is as small as an hour and also can be upto month time.
Sunspot
Active region
on the Sun
Maunder Butterfly Diagram
Observation of Sunspot
Effect on Earth
Formation of Aurora in high latitudes near magnetic poles
Formation of Sunspot
Magnetic field lines in Sunspot
Solar Wind and Earth
Aurora
Life Cycle of Sun/Possible end of Sun