Brief About Solar System

Topics:

  • What is Solar System?
  • Theories of Origin of the Earth
  • Modern Theory of Origin of the Universe
  • What is Galaxies, Star, Planet and Satellite?
  • Solar System Facts
  • About Sun
  • Structure of the Sun
  • Inner Planets & Outer Planets
  • Detail Discussion on 8 Planets and Solar System
  • Dwarf Planet

 

Solar System

What is the Solar System?

A solar system consists of a star at the centre and the eight planets, moons, asteroids, comets and meteoroids that revolve it.

Note: Solar systems can also have more than one star. These are called binary star systems.

Theories of the Earth’s Origin:

There are many theories supporting the origin of the earth.

Nebular Hypothesis:

One of the earlier and popular arguments of the earth’s origin was by a German professor Immanuel Kant. Mathematician Laplace revised It in 1796. It considered that planets were formed out of a cloud of material associated with a youthful sun, which was slowly rotating.

 

Lyttleton propounded the accretion theory of the earth’s formation. According to this theory, approximately 4.6 billion years ago, the solar system was a cloud of dust and gas known as a solar nebula.

 

What is Universe?

The Universe is a vast endless space which includes galaxies, stars, planets and other forms of matter and energy in it.

Modern Theory of Origin of the Universe:

The most popular argument regarding the origin of the universe is the Big Bang Theory. It is propounded by Abbe Georges Lemaitre in 1927, a Belgian astronomer.

The Big Bang Theory is also called expanding universe hypothesis. According to it, the universe was formed during a period of inflation that began about 13.75 billion years ago.


What is Galaxies?

Galaxias (Greek): “milky”, a reference to the Milky Way.

A galaxy is a system of billions of stars, stellar remnants, interstellar gas, dust, and dark matter.

The Milky Way is the galaxy that contains our Solar System.

 

Galaxies are in three major forms:

1. Spiral Galaxies: It consists of a flat and rotating disk of stars, gases and dust. It has a central concentration of stars known as the ‘bulge’. The Milky Way and the Andromeda are spiral galaxies.

2. Elliptical Galaxies: It contains older stars with fewer gases. Messier89 galaxy is an elliptical galaxy.

3. Irregular Galaxies: They are youthful galaxies with more dust and gases. This can make them very bright. Large Magellanic Cloud is an example of irregular galaxy.

 

Note: In fact, the stars, planets and galaxies that can be detected make up only 4 percent of the universe, according to astronomers. The other 96 percent of the substances in the universe cannot be seen or easily understandable.

 

What is Star?

A star is type of astronomical object which has its own light and heat. e.g. The nearest star to Earth is the Sun.


What is Planet?

Planet in Greek means ‘wanderer’.

Planet is the celestial body which does not have light or heat of its own.

What are the qualities of Planet?

  • It should orbit around the sun.
  • It should not be a satellite of any planet.
  • Due to its own mass and self-gravity, it should get a spherical shape and
  • Any other celestial body should not cross in its orbit.

 


Solar System Facts:

A solar system consists of a star at the centre and the eight planets, moons, asteroids, comets and meteoroids that revolve it.

  • Eight Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
  • They revolve around the Sun in fixed elliptical paths known as ‘orbits.
  • Our solar system orbits the centre of the Milky Way Galaxy at about 828,000 km/hr.
  • Our solar system takes about 230 million years to complete one orbit around the galactic centre.
  • The solar system is believed to have been formed about 4.6 billion years ago.
  • Kuiper Belt: This is a sparsely occupied ring of icy bodies. (Appear after Neptune). This is almost all smaller than the dwarf planet Pluto.
  • Oort cloud: Beyond the fringes of the Kuiper belt. The Oort cloud is made up of icy pieces of space debris. It is orbiting our Sun as far as 1.6 light years away.

 

About Sun:

  • The Sun is at the centre of our solar system.
  • It is a yellow dwarf star, with a hot ball of glowing gases.
  • The Sun is made up of about 70.6% hydrogen, 27.4% helium and 2% other gases.
  • Its gravity holds the solar system together and it keeps everything from the biggest planets to the smallest particles of debris in its orbit.
  • Electric currents in the Sun generate a magnetic field that is carried out through the solar system by the solar wind.
  •  At the core, the temperature is about 15 million°C.

 

Structure of the Sun:

There are three main layers in the Sun's interior:

The Core

The Radiative zone, and

The Convective zone.

The core is at the centre.

The Core:

It is the hottest region, where the nuclear fusion reaction to give the sun power.

The Radiative zone:

Its name is derived from the way energy is carried outward through this layer, carried by photons as thermal radiation.

The Convective zone:

It is also named after the dominant mode of energy flow in this layer. The boundary between the Sun's interior and the solar atmosphere is called the Photosphere.

 

Photosphere:

  • The solar atmosphere is called the Photosphere.
  • It is what we see as the visible ‘surface’ of the Sun.
  • The temperature of the Sun’s surface is about 5,500ºc to 6,000 ºc.

 

Chromosphere:

The lower region of the solar atmosphere is called the Chromosphere. Its name is derived from the Greek word chroma (meaning colour), for it appears bright red when viewed during a solar eclipse.

 

Corona:

The uppermost portion of the Sun's atmosphere is called the corona, and is surprisingly much hotter than the Sun's surface (photosphere).

The upper corona gradually turns into the solar wind. Solar wind is a flow of plasma that moves outward through our solar system into interstellar space.

 


Detail Discussion on 8 Planets and Solar System:

Planet:

The word planet in Greek means ‘wanderer’.

Planet is the celestial body which does not have light or heat of its own.

What are the qualities of Planet?

a. It should orbit around the sun.

b. It should not be a satellite of any planet

c. Due to its own mass and self-gravity, it should get a spherical shape and

d. Any other celestial body should not cross in its orbit.

 

What is the Planet Day and Planet Year?

Each planet spins on its own axis. This movement is called rotation. One rotation makes one ‘planet day’.

The planets moving around the sun is called revolution or a ‘planet-year’.

 

The MERCURY:

  • It is the nearest planet to the Sun.
  • There is No Life, No Water.
  • The smallest planet in the solar system.
  • Not have any satellite.
  • In 88 Earth days to complete one revolution around the sun (Shortest Revolution).
  • The sunlight takes 3.2 minutes to reach to Mercury.
  • Mercury is the second hottest planet though it is nearest to the sun.

 

The VENUS:

  • It is second nearest to the sun.
  • It is known as ‘Earth’s Sister’ planet due to its similar size and mass as that of our Earth.
  • Venus is the hottest planet in the solar system  (462°C.) (90-95% CO2).
  • Venus is known as “Morning star and Evening star”.
  • Unusual Rotation: Only Venus and Uranus have this ‘backwards’ rotation.( rotate East to West)
  • Venus take 224.7 Earth days to complete one revolution around the Sun.
  • The sunlight takes 6 minutes to travel from the sun to Venus.

 

The EARTH:

  • Earth is the third nearest planet to the sun.
  • Fifth largest planet.
  • The Earth takes 365.25 days to complete one revolution around the Sun.
  • The densest planet in the solar system.(5.52 gm/cm3).
  • Life, Atmosphere with Oxygen and Water.
  • The ‘Blue Planet’ /Water Planet.
  • Only one natural satellite called the Moon.
  • The sun light takes about 8.2 minutes to reach the earth.

The MARS:

  • Mars is the fourth nearest planet to the Sun.
  • Second smallest planet.
  • Due to the presence of iron oxide, It is known as “Red planet”.
  • Mars probably is the most hospitable to life (Possibility of Life).
  • The angle of inclination and period of rotation (24 hours and 37 Minutes) of Mars is similar to that of the Earth.
  • Its takes 687 days to complete one revolution around the Sun.
  • Like Earth, Mars has seasons, polar ice caps, volcanoes, canyons and weather.
  • Mars has two satellites namely Phobos and Deimos.

 

The JUPITER:

  • Jupiter is the largest planet.
  • It is fifth planet from the sun.
  • Made primarily of gases and is therefore known as ‘Giant Gas planet’.
  • It takes 11.86 years to complete one revolution.
  • Jupiter has the shortest day in the solar system (Fastest rotational Velocity).
  • Jupiter has 67 confirmed satellites orbiting the planet.
  • Ganymede is the largest natural satellite in the solar system (even bigger than the planet Mercury).

 

The SATURN:

  • Saturn is the 6th planet from the Sun.
  • Second largest planet in the solar system.
  • Saturn is called as the Ringed Planet (large & beautiful ring systems that encircles the planet).
  • Saturn is the only planet whose average density is less than water.
  • The Saturn has 30 rings and 53 confirmed natural satellites.
  • it takes 29.4 years to complete one revolution around the sun.

 

The URANUS:

  • Uranus is the seventh planet from the sun
  • Not visible to the naked eye.
  • Like Venus, Uranus also rotates on its axis from east to west.
  • Hydrogen, helium and methane are the major gases of its atmosphere.
  • It is very cold due to its great distance from the sun.
  • Uranus : Greek god of the sky.
  • It has a dense atmosphere primarily consisting of methane, which lends it a bluish-green appearance.
  • Uranus also has rings and twenty-seven satellites.

 

The NEPTUNE:

  • Uranus & Neptune is known as ‘Twin Sister’ like Earth and Venus.
  • Neptune is the 8th  planet from the sun.
  • it takes nearly 165 years to revolve around the sun.
  • It has 13 natural satellites and 5 rings.
  • It is the coldest planet in the Solar System because it is the farthest planet from the Sun.
  • Neptune was the first planet located through mathematical calculations.
  • Neptune is our solar system’s windiest planet.

 

What is Dwarf Planets?

Dwarf planets are tiny planets in our solar system.

Any celestial body orbiting around the sun, weighing for the self gravity and nearly be round in shape is called ‘Dwarf Planet’.

It should not be a satellite of any planet.

They are five in number Ceres, Pluto, Heumea, Makemake and Eris.

As Pluto has not cleared the neighbourhood around its orbit, it is officially demoted in 2006 from its ninth position as a planet.

 


Practice MCQ:

Que 1. Which is the hottest and coldest planet of the solar system?

  1. Venus and Uranus
  2. Mercury and Neptune
  3. Venus and Neptune
  4. Mercury and Uranus

Que 2. Asteroids found between orbits of

  1. Jupiter and Saturn
  2. Uranus and Neptune
  3. Neptune and Pluto
  4. Mars and Jupiter

 

Que. The scientist who proposed Big Bang Theory was

a. Abbe Georges Lemaitre

b. Edwin Hubble

c. Nicholas Copernicus

d. Aryabhatta

 

Comment Answer…

 

Source: NCERT

 

 

 

 

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