Universe and the Origin of the universe
Universe - The limitless expanse of space surrounding us consisting of planetary systems, stars, galaxies, etc is called universe.
It has 100-400 billion galaxies with each galaxies containing 100-400 billion stars.
Origin of the Universe
Steady state theory - It was proposed by Hoyle. According to the theory the overall size and mass of the universe remains constant at any point of time and the universe has no beginning and no end. But it is always expanding creating new stars and galaxies at the same rate old ones becomes unobservable. (There is some kind of boundary within the universe is defined and whatever goes out will not be observable)
Pulsating theory - It is proposed by Eddington. As per the theory, the universe expands because of explosion and contracts because of gravitational pull. The universe is currently in the phase of expansion.
Big Bang theory - It was proposed by Lamaitre in 1927. As per the theory, before 13.7 billion years the universe was extremely compact, dense and hot singularity. A cosmic explosion happens 13.7 years ago which was called Big bang. From that time universe started to expand and still continue expanding today. This expansion subsequently led to the formation of atoms, molecules, stars, galaxies, etc.
In 1929, Hubble proposed that all observable stars and galaxies are moving away from the Earth. He discovered this through the phenomenon called Red Shift. The rate of expansion is called Hubble's constant.
- Red shift - if a body moves away from the observer
- Blue shift - if a body moves towards the observer
Origin of Stars
Nebula - It is a giant cloud of gas and dust mainly consisting of hydrogen. The gaseous particles are pulled together by gravity and the gaseous cloud starts to spin.
Protostar - The spinning gaseous mass when it reaches high temperature with the formation of hot core is known as protostar.
Birth of Star - When the temperature crosses 15 million degrees, nuclear fusion reaction starts at the core and the birth of star happened.
Red giant - When the supply of hydrogen runs out, core of the star contracts and simultaneously the outer shell expands resulting in increase in the size of the star. It is called Red giant.
If it is a low mass star with less than 10 times the mass of the sun, the core collapses leading to the formation of planetary nebula with a spherical shell of gases which over the period of time will be left with only the core which is called as White dwarf which may become black dwarf in future.
where as if the initial mass of the star is more that 10 times the mass of the sun, it becomes Red Super giant with huge size. All the red super giant will result in Supernova due to the explosion of iron core. After the supernova explosion, if the remnant core is between 1.3 to 3 times the mass of the sun, it leads to the formation of Neutron Star which is a very high density body composing of closely packed neutrons. Whereas if the remnant core after supernova explosion is more than 3 times the mass of the sun, the core collapses under the gravity leading to the formation of Black Hole with infinite gravity and density.
Galaxy - The sprawling system of gas, dust and stars held together by gravity is called as galaxy. All galaxies contain a super massive black hole at the centre.
Types of Galaxy -
- Elliptical Galaxy - It is round or oval in shape with stars distributed uniformly throughout.
- Spiral Galaxy - It is relatively flat disc with a central bulge and spiral spiral arms.
- Irregular Galaxy - It has no definite shape or structure.
Milky way is a Spiral Galaxy in which Sun is located in one of the spiral arm (Orion Arm) and blackhole at the centre named 'Sagittarius'.
Nearest galaxy - Andromeda
Twinkling of Stars - Due to the turbulence in the atmosphere, light coming from stars are more deflected as it appears to come from a point source.
However, the light coming from different planets of the solar system is not from a point source and don't get deflected easily. That's why planet don't twinkle.
Note - Twinkling of stars is not observed in space because of the absence of atmosphere in space.
Light year - It is the distance travelled by light in 1 year. It is used to measure distance between different stars.
PYQ
Which one of the following is a reason why astronomical distances are measured in light years?
a) Distances among stellar bodies doesn't change.
b) Gravity of stellar bodies doesn't change
c) Light always travels in straight line
d) Speed of light is always same.
Ans - c
Constellation - A group of stars forming recognizable pattern in the sky is called constellation.
Pole star - Stars which are aligned with the axis of rotation of the Earth is called as pole star, i.e., they are exactly above the poles.
In the Northern hemisphere, we have North Pole Star which is known as Polaris and in the Southern hemisphere, it is Sigma Octantis.
Pole stars always appear to be fixed in the sky. However, the angle at which it is visible in the sky increases from equator to the poles.
Solar System
Solar System - The sun and other celestial bodies revolving around it which includes planets, satellites, asteroids, comets, meteors, etc constitute solar system. Its average age is about 4.8 billion years.
Next Article - Solar System
Notes on other subjects
Optional Notes
Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own.
Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍
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