THE UNIVERSE

WELCOME TO THE UNIVERSE

We are going to see about "THE UNIVERSE"




THE SPACE

Space extends to infinity in all directions.

      Space Probe Mariner 10 gave valuable information about Venus and Mercury in 1979.

Space is the vast region with no known boundaries beyond the Earth's atmosphere. The Space is the empty area extending in all directions to infinity.
The Solar system, the stars,galactic dust and galaxies regions between the Galaxies all form parts of the space. It has no automosphere. It appears black during the days as well as at the night.It does not inhabit any living organism.



Man Has been trying to collect information about the Space with help of powerful radio telescopes, rockets, Satellites, Space crafts and space probes. The Space explorations have revealed many mystries of the space and enhanced the man's knowledge about it.

THE STARS
The Stars are huge spheres of glowing gases. Stars vary considerably in size, colour, temperature, brightness and distance from the Earth. The sun also a medium sized star. It is comparatively nearer to the earthvhence it looks blgger in Size.

Stars appear to twinkle because they are seen though the earth's atmosphere. The stars also seen to move from east to west across the Space. This "Movement" is actually caused by the spinning of the earth. Stars are often classified according to their size.




The four major size are super giant, medium and dwarf. The Colour of the star indicates its surface tempertaure.The hottest stars are blue. Red Stars are somewhat cooler having a temperature of about 2800 OC. The Sun and other yellow stars havesurface temperature of about 5500 OC. Rigel the blue-white giant star has a diameter 80 times larger than that of the Sun and is 60,000 times brighter.

A Spacecraft takes three days to reach the mon from the earth. It will take sevral months to reach the sun and may take thounds of years to reach the nearest star. Such long distances covered in months and years are very difficult to be measured in kilo meters.

Therefore scientists use units like light year and  parsec (PC) for measuring the distances of stars. A light year is the distance travelled by light in one year at a speed of 3,00,000 km per second.
                                         12
It is equal to 9.4607 x 10    km. 1 Parsec is eual to 3.26 light years 
                        12
or 30.857 x 10   km. It takes 1.3 seconds for the moonlight to come to us. The Sunlight reaches the earth in 8 minutes 18 seconds. It should take 4.2 light years for the light to reach the Earth from Proxima Centauri, the nearest star next to the sun. The fartherest star in our  galaxy lies at a distance of about 63,000 light years (19.325 Parsec.)


Plusars, Blackholes and Quasars

Pulsars
Pulsars are rapidly spining stars that emitpulses of radio waves at regular intervals. The word pulsar stands for pulsating radio Star.
When a big star explodes, its outer shell scatters to form a nebula while is core contracts into a denser star called the neutron star.

Its neturons are  tightly compressed and it has extremely high density. Neutron Stars are very small and dull. Average diameter of a neutron star is 10 km. These neutron stars are called pulsars.

Radio pulses coming from pulsars  pro due "Tick" like sound  on radio telescope. The neturon stars are like lighthouses in the space. Ordinary pulsars flash at an interval  of every one or half a second. The most rapid flashing pulsar NP 0532 lies in the Crab Nebula and emits 30 pulses per second.
The oldest and the least frequency pulsar is NP 0527 which emits pulses at a rate of one pulse per 0.03 second to one pulse per 4 seconds. Most of the pulsars are not visible through optical telescopes. They may be observed with the help of radio telescopes.

Only two pulsars-NP 0532 in the Crab Nebula and PSR 0833-35 in Gum Nebula can be seen with the help of optical telescope. Scientists have so far discovered more than 100 pulsars.

Blackholes
When very big stars, three times bigger than the sun, Collapse by the force of their own gravity, some black regions are created in the space. these are called black holes. They have gravitational force so enormously high that no matter, not even light can escape from it.

The first black hole was deteched in 1972. It was in a binary star of Cygnusx-1 Which is a powerful source of X-Rays and infrared radiation which help in their detection in the space. The mass of black holes may be equal to that of 100 million Suns.


Quasars

When a star has consumed its hydrogen, its outer shell swells and it turns red. It is considered the stage of collapse of the star. After explosion the star disappears leaving behind a black hole.

Quasar is an abbreviated form of Quasi Stellar Radio Sources. Quasars appear like a star. Through an optical telescope they look like an ordinary dull star, but radio telescope observations have indicated that they are the the source of radio waves.

Quasar 3C-273 was dicovered by Maarten Schmidt in 1962. The value of its red-shift was 0.185. Red-Shift is an effect of change in frequency and is seen in moving objects. If the object is moving away, its light will shift to the red end of the spectrum. Red-shift indicates that the source of light was receding away.

Quasars emit radio waves and X-Rays with light. The size of a Quasars is 1/100,000 of our galaxy but its  brightness is 100-200 times more. So far 1500 quasars have been discovered.