the universe1

7/27/2019 The Universe1

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The UniverseBy Praveen kumar Reddy


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Universe is Awesome


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How stars formed ?

How do they shine ?

Physical and chemical properties

of these stars

.and many more


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First we will understand our Nearest star

SUN


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sun

It is the nearest star

It is very bright and has high temperature


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Distance of sun from Earth is nearly

1.5 x 10 ^8 kilometers.

sun


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It takes 8 minutes to travel light from the sun

to the Earth.

sun


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Mass of sun is calculated from Kepler laws

Mass of sun is 2 x 10^30 Kg

It is 3 x 10^5 times that of Earth

sun


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Surface temperature of sun is about 6000 K

sun


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The amount of energy radiated per second by the

sun in all directions are called solar luminosity.

It is represented by 3.9 x 10^26 watt

sun


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Solar observatories in india

Kodaicanal

Udaypur


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Sun rotates from West to East.

Sun rotates itself in 26 days

sun


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Solar spectrum posses dark lines called Fraunhoffer

lines.

Study of these lines shows existence of elements like

Sodium , calcium in addition to hydrogen in the sun.

sun


15/49Structure of sun


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Cross section of sun

The visible disc of sun is called photosphere


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Layer just above photosphere is called

Chromosphere.

It extends 10000 km above photospehre

It is brighter but less dense than photosphere.



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Region beyond chromosphere is called Corona.

It extends to million of kilometers

This region seen as white halo around sun during eclipse.



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Matter in this region is in plasma state. And the temperature

is of the order of few million degrees.

sun


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In photosphere grain like patterns observed

called granulations.

sun


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We can also observe thread like structures called spicules.

Some matter stream out of suns surface in bursts , these are

called solar flares.

sun


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When image of sun is obtained by telescope ,

is projected on white screen dark irregular

patches observed on sun . They are called

sun spots.

sun

Temperature at sun spot is around

4000 K and the temperature of

photosphere is around 6000 K


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Aurora or polar lights

Charged particles eject from sun , ionize air

molecules which results in spectacular color display.

These are seen in polar regions.


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Sun emits electro magnetic radiation like

x- rays , ultraviolet.

But we receive only heat , light , radiowaves and small amount of ultraviolet.

This is because absorbed by earths

atmosphere.

sun


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Enormous energy is due to nuclear reactions

taking place in interior of sun.

Temperature of sun is about 20 million

degrees.

Energy released reaches photosphere by

radiation and convection.

sun


26/49Stars


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Stars

Night sky is sprinkled with an enormousnumber of stars that appear as bright points.


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Brightness and features of the spectrum can

be determined by using telescopes and other

instruments.

Stars


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Telescopes help in learning about

1. size

2. Mass3. Temperature

4. Composition

5. Evolution of stars

Stars


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Stellar distances are very large , a unit called

Parsec.

1 parsec =3.26 light years.

Stars


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Some stars are bright , some are dim , some stars look white,

while some look blue and while some look like red.

Stars


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Brightness of stars are represented by

magnitude scale.

Star Magnitude

How Much Brighter

than a Sixth Magnitude

Star

Logarithmic scale of

2.512 X between

magnitude levels

Starting at Sixth

Magnitude

1 100 Times

2.51 x 2.51 x 2.51 x 2.51 x

2.51

2 39.8 Times 2.51 x 2.51 x 2.51 x 2.51

3 15.8 Times 2.51 x 2.51 x 2.51

4 6.3 Times 2.51 x 2.51

5 2.51 Times 2.51 x

6


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Total energy emitted by star in one second is

called luminosity.

It depends on the temperature and diameter

of the star.

Stars


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Luminosity of the star can be

expressed in terms of the

luminosity of the sun.

Example luminosity of Sirius

is 23.5 times the luminosity

of the sun.

Stars


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Spectrum of star is like that of sun is a

continuous spectrum crossed by dark

absorption lines.

Analysis of these lines helps to identify the

elements present in stellar atmosphere.

Stars


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Surface temperatures of stars range from

about 2000K for reddish stars to about 50000K

for bluish white stars.

Stars


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Size of stars

Radius of star can be deduced from luminosity and

temperature. Majority of stars have radius in the range of one

tenth to twenty times the solar radius.


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When two stars of gravitationally bound

system and go in circles around their common

center of mass.

Their individual masses can be obtained by

observing their motion.

Such a star system is called binary star.

Mass of stars


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Mass of stars


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Mass of stars

Luminosity of star increases with mass.

Stars about fourty times heavier than the sun are roughly

million times luminous of the sun.


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Stellar interiors

Knowing their size and mass , mean density

can be calculated.

Density of stars vary from 5 x 10^-4 kg to 10 x

10^-4 kg.


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Central temperature ranges from 10 to 30 million

degrees as we go from the coolest to the hot stars.

Stellar interiors


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They are some strange type of stars

White dwarfs


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Red giants


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White dwarfs


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Black dwarfs


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Neutron stars



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Black holes


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Super nova

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