Friday, 30 September 2016

The Solar System - Geography


The Solar System - Geography for Bank PO, Clerk, SSC CHSL, CGL and other competitive exams| Universe, Galaxy, Stars, Solar System, Sun, Planets, Pluto


• The universe is commonly defined as the totality of everything that exists including all physical matter and energy, the planets, stars, galaxies and the contents of intergalactic space.

• The study of universe is known as Cosmology.
→ Literal meaning of Cosmology
cosmos (universe) + logos (science)


• A galaxy is a collection of billions of stars, dust, gas, clouds that hold together by force of gravity. Examples are the Milky Way, Andromeda galaxy etc.

• Milky Way or Akashganga is our home galaxy. It is spiral in shape.

• There are about 100 billion galaxies (1011 galaxies) in the universe, and each galaxy has, on an average, 100 billion stars (1011 stars).


• Stars are formed by clumps of dust and gas in a nebula come together due to gravity.

• Due to high temperature hydrogen converts to helium and heat and light is emitted and form stars.

• Stars emit light of their own (self luminous bodies).

• Light takes about 4.3 years to reach us from the next nearest star proxirna centauri.


• A constellation is a group of stars that forms a recognizable pattern in the night sky.

• Usually, they are named after mythological characters, people, animals and objects.

• Ursa Major or the great bear is a such constellation.
→ Big dipper or Saptarishi is a group of seven stars visible in the northern hemisphere is a part of Ursa Major.

Solar System

• The sun along with its eight planets, asteroids and comets form 'solar system'.

The Sun:
→ The Sun contains 99.85% of the solar system's mass.
→ It is in the center of the solar system.
→ It is made up of extremely hot gases particularly hydrogen.
→ The Sun has a diameter of roughly 14 lakhs kilometers which is almost 110 times the diameter of the Earth.
→ The sun weighs 2 × 1027 tonnes.
→ The sun is about 150 million km away from the earth.
→ It takes 8 minutes for light reach Earth from the Sun.
→ The surface temperature of sun is 6000° C.
→ Temperatures inside the Sun can reach 150 lakhs degrees Celsius.
→ The shining surface of the sun is called 'Photosphere' which look like a disc and acts as a source of energy.
→ The outer layer of sun's atmosphere made up of thin hot gases, is called Corona.

→ Asteroids are minor planets lying between the orbit of Mars and that of Jupiter.
→ These revolve around the sun in the same way as the planets.
→ These are made up of rock and metal.
→ 'Ceres' whose length is about 1000 km is the largest one.
→ More than 5000 asteroids have been identified.

→ Comets are small, icy objects that orbits the sun.
→ Comets have highly eccentric elliptical orbits
→ When passing close to the Sun, solid frozen part heats up and vaporizes to form a gaseous luminous coma and sometimes also a tail.

Meteors and Meteorites:
→ The meteors are the remains of comets which are scattered in the interplanetary space of the solar system.
→ On contact with the earth's atmosphere, they burn due to friction.
→ Those which completely burn out into ash are called meteors or 'shooting star.'
→ Those which do not burn completely and strike the earth in the form of rocks are called 'meteorites'.

→ Planets are opaque bodies which continuously revolve around the sun.
→ There are eight (8) planets in the solar system.
→ These planets move around the sun in fixed paths called orbits.
→ The sequence of planets according to their distance from the sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
→ The sequence of planets according to their size is: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars and Mercury.

Classification of Planets:
→ The solar system's eight planets is divided into two groups according to some common features:
◘ Terrestrial Planets or Rocky Planets: Mercury, Venus, Earth and Mars.
◘ Jovian Planets or Gaseous Planets: Jupiter, Saturn, Uranus and Neptune.
→ Planets are classified into two groups: inner and outer planets as per separation by Asteroid Belt.
→ Difference Between Inner Planets and Outer Planets:

Inner Planets  Outer Planets 
These are nearer to the sun. These are far away from the sun.
These include Mercury, Venus, Earth, Mars. These include Jupiter, Saturn, Uranus Neptune etc.
These are made up of dense metallic minerals. These are made up of hot gases, mainly hydrogen and helium.
These move faster and have a shorter period of revolution. These move rather slowly and have a longer period of revolution.
These have thin, rocky crust.  These are all gaseous bodies.
These have a mantle rich in iron and magnesium.  These are made of gases. 
These have a core of molten metals and have thin atmosphere. These have ring systems around them.
These have very few natural satellites (or moons) or no satellites  These have a large number of natural satellites (or moons). 

→ Mercury is the smallest and the nearest planet to the Sun.
→ It is extremely hot planet.
→ This planet has no water in it.
→ It has no atmosphere and no satellite.
→ Its days are scorching hot and nights are frigid.

→ Venus is second planet according to distance from the sun and also very close to earth.
→ It is considered as 'Earth's-twin' because its size and shape are very much similar to that of the earth.
→ It is also the brightest planet.
→ It is also called the 'morning' or 'evening star'.
→ It is probably the hottest planet because its atmosphere contains 90-95% of carbon dioxide.
→ The day and night temperatures are almost the same.
→ Venus has no water in it also there is no sufficient oxygen present.
→ It has no satellite.

→ The earth is the third nearest planet to the Sun.
→ Earth is the only known planet which provides sustenance or life on it.
→ It takes 23 hours 56 minutes and 4.091 seconds to rotate on its axis.
→ It takes 365 days, 5 hours and 48 minutes to revolve around the Sun. 
→ he earth is called 'blue planet' because because its two-thirds surface is covered by water. From the outer space, the earth appears blue 
→ It has a large quantity of oxygen which supports life.
→ The earth has all the essential elements like carbon (in the form of CO2), hydrogen (H2), nitrogen (N2) and oxygen (02) which act as building blocks for the origin of life. ›
→ The earth is neither too hot nor too cold. It has Goldilock Zone

Goldilock Zone is the habitable zone of solar system where all conditions are available for life to sustain. 

→ The earth has a protective layer of ozone which save life from the harmful ultraviolet radiation of the sun.
→ The earth has a satellite: Moon
◘ The moon is the only satellite of the earth.
◘ Its size is approximately one-fourth (27%) that of the earth.
◘ It has a diameter of 3475 km.
◘ The moon moves around the earth in about 27 days. It takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth.
◘ The moon's surface is covered with dead volcanoes, impact craters, and lava flows.
◘ The moon has no atmosphere, no twilight and no sound.
◘ The bright parts of the moon are mountains whereas the dark patches are low-lying plains.

→ Mars is considered as 'Red Planet' because of iron-rich red soil and pink sky.
→ It is marked with dormant volcanoes and deep chasms where once water flowed.
→ It has a thin atmosphere comprising of Nitrogen and Argon.
→ The highest mountain name of Mars is Nix Olympia which is three times higher than Mount Everest.
→ 'Phobos' and 'Demos' are two satellite of the earth.

→ It is the largest planet of the solar system.
→ Its atmosphere contains hydrogen, helium, methane and ammonia.
→ It is also known as winter planet as its average temperature is very low (-148° C).
→ It also contains dusty rings and volcanoes.
→ It has 16 satellites.
→ Ganymede, satellite of Jupiter is the largest satellite in the Solar system.

→ Saturn is the second largest planet of the solar system.
→ It has a bright concetric rings composed of thousands of rippling, spiraling bands of icy rock and dust just 200 feet thick and 270,000 km in diameter.
→ It has 21 known satellites. Titan is the largest among them.

→ Uranus is the third biggest planet of the solar system. It is about four times the size of the earth.
→ The planet appear greenish in colour because of methane gas present in its atmosphere.
→ Uranus rotates from east to west axis, which is opposite to other planets except Venus.
→ It is one of the coldest planets because of having an average temperature of -223° C.
→ Its atmosphere is made of mainly hydrogen and helium
→ The Uranus appear blue-green colour due to presence of methane.
→ There are 9 dark compact rings around the planet and a corkscrew shaped magnetic field.
→ It has 15 satellites. Aerial, Ambrial, Titania, Miranda are important satellite.

→ It is the most distant planet from the sun.
→ The temperature on the surface of Neptune remains low.
→ There are five rings of Neptune. The outer ring seems to be studded with icy moonlets while the inner ring appears narrow and nearly solid.
→ It has 8 satellites like Titron, Merid, N-1, N-2, N-3 etc.

Why Pluto was demoted from Planets?

• Pluto, demoted from planet status in August 24, 2006 under new IAU (International Astronomical Union).

• Now, Pluto and other dwarf planets like it will be called plutoids. 

• Plutoids are celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their hydrostatic equilibrium (near-spherical) shape. The two known plutoids are Pluto and Eris. It is expected that more plutoids will be named as science progresses and new discoveries are made.


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