UNIVERSE: Solar System, the Sun, Planets, the Moon

Universe-Solar System, Sun, Moon, Planet

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Universe | Solar System, the Sun, Planets, the Moon

The Universe is defined as the totality of everything that exists, the planets, stars, galaxies, all physical matter, energy, and the contents of intergalactic space. The study of the universe is known as Cosmology. The universe comprises billions of galaxies, particles, cosmotic material, etc. It is believed that 4,600 million years ago stars and planets were formed from a giant cloud of gases and tiny dust particles known as nebula, a Latin word meaning dust and cloud.

The galaxies are made up of millions of stars held together by the force of gravity and these stars account for most of the masses of the galaxy. Our own galaxy is called the Milky Way (or the Akash Ganga) and it contains billions of stars among which the Sun is also the one. The Milky Way is named so because it is like a white band. Planets and other objects revolve around the Sun and make up the Solar System with the Sun at the center. Andromeda is our nearest galaxy.

Structurally, there are three forms in which galaxies are present:

  1. Elliptical galaxies– They are without spiral arms and have ellipsoid shape.
  1. Irregular galaxies– They have no shape.
  1. Spiral galaxies-They have a central nucleus with great spiral arms. Milky Way and Andromeda are some examples.

Evolution of Universe

The three main theories put forward to explain the origin and evolution of the universe are

  1. Big Bang Theory– It was proposed by Georges Lemaitre and is believed that the explosion of a hot ball of matter with a big bang lead to the creation of energy, matter, time and space. The big bang further released gases like hydrogen and helium. Later this created the universe including stars, planets, particles, galaxies etc.
  2. The Pulsating Theory According to this theory, the universe is supposed to be expanding and contracting alternately i.e, pulsating. At present, the universe is expanding.
  3. Steady State Theory Bondi, Gold and Frd Hoyle developed this theory. It states that although the universe is expanding, it nevertheless does not change its appearance over time and it has no beginning and no end.

An individual organization namely the Cosmic Background Explorer (COBE) and missions such as the Wilkinson Microwave Anisotropy Probe (WMAP) have been launched by NASA to study the radiations and transformations present in the universe.


Stars are heavenly bodies made up of hot burning gases which produce their own light. They are huge burning balls of hot gases which are self-luminous and shine in space. They twinkle because light from the star has to pass through different layers of the atmosphere with varying densities.

Neutron stars are formed by Supernova explosions, which are huge in size with approx 18 km diameter and a mass 1.4 times that of the Sun. A pulsar is one such highly magnetized and rotating neutron star. The nearest star to the sun is the Proxima Centauri, which takes four years for its light to reach us.

A star’s color indicates the temperature of its surface, blue color denoting maximum temperature, white, yellow, orange, red stars have a sequentially declining range of temperatures.

Constellation is a stars group or pattern collectively forming fantastic patterns or designs of creatures, brave heroes, heroines, monsters, etc. Many have legendary backstories mostly of courage, beauty, etc. Some of the most popular constellations are the Big Bear or Ursa Major, Small Bear or Saptarishi are very easily recognizable in the sky. Saptarishi as its name is a group of seven stars. The Pole Star or North star always stays in the same position and helps in determining the north direction.

Concept of Black Hole and Chandrasekhar Limit

  • A reowned Indian Physicist Chandrasekhar has predicted an upper limit to the mass of stars, which is called as Chandrasekhar limit. It is 1.44 times the mass of the Sun.
  • Above the upper limit, two conditions are possible.
    • Explosion of the star to form neutron star.
    • Collapse and compaction of the stars to form Black Holes.

The black holes are formed due to collapse and compaction under gravity, at the end of the life cycle of a star.

Some of the units used for the calculation of distances in-universe are as follows:

Units of Distance

UnitDescription of the Unit
Light yearIt is the distance that light can travel in 1 year. It is equal to almost 9.46 × 1012km.
Astronomical unit It is the average distance between the Sun and the Earth. 1 AU=150 million km
ParsecIt is the distance from the Earth to a star that has a parallax of 1 arc second. The actual length is about 3.262 light-years.
Units of Distance

UNIVERSE: Solar System

The solar system is a family comprising of the Sun, 8 planets, their satellites, and other non-stellar objects, which are believed to have been developed from the condensation of gases and other lesser bodies. The word ‘Solar’ is derived from the Latin word ‘Solaris’ which means sun.

The end of the Solar System is about 122 AU (Astronomical units) away from the Sun.

Components of the Solar System

Our Solar System consists of

  • The Sun , eight planets (including Pluto) and their respective satellites.
  • Interstellar debris such as asteroids, meteroids, comet.
  • The electrically charges gases, called Plasma.
  • Interplanetary dust particles.
  • The components of Solar System other than planets, dwarf planets and satellites are called as Small Solar System Bodies (SSSB).
Universe- Solar System
Picture Credit-en.wikipedia.org

Origin of the Solar System

Various theories were given to explain the Origin of the Solar System.

Gaseous HypothesisKant
Nebular HypothesisLaplace
Planetesimal HypothesisChamberlin and Moulton
Tidal HypothesisSir James Jeans and Harold Jeffreys
Binary Star HypothesisHN Russell
Supernova HypothesisF Hoyle
Interstellar Dust HypothesisOtto Schmidt
Electromagnetic HypothesisH Alfven
Proplanet HypothesisDr. Von Weizsacker and G Kuiper
The hypothesis with their Propounders


The Sun being the center of the Solar System is the major source of energy, provided by the nuclear fusion reaction, that converts hydrogen into helium in the core of the Sun. Hence, the Sun is majorly comprised of hydrogen and helium.

It accounts for more than 99 percent of the mass of the Solar System and due to this, the Sun exerts an immense gravitational pull on the planets to keep them rotating around its indefinite elliptical orbit. This pull keeps all the planets and satellites revolving around it.

The glowing surface of the Sun that we see is called Photosphere. Above the photosphere is the red-colored Chromosphere and beyond it is the magnificent corona, which is most easily visible during eclipses.

The Sun has a surface temperature of about 6000°C and the interior is at 20 million degrees Celcius.

It takes 224 million years to complete one circle (revolution) around the center of the Milky Way. This is known as a Cosmic year. It takes approximately eight minutes for the sunlight to reach the earth’s surface.

Superimposed on Sun’s white light are hundred of dark lines called Fraunhofer lines. Each line indicates some elements existing as gases in the Solar System.

Concept Associated with the Sun

  • Solar Winds The Sun is continuously emitting streams of photons in all emitting streams of photons in all directions either as spiral streams called Solar Wind or bouts of incandescent material called Solar Flares.
  • Aurora The constituent particles of the solar wind are trapped by the earth’s magnetic field and enter the Earth’s upper atmosphere as Aurora. It is described as Aurora Borealis in the Northern hemisphere and Aurora Australis in Southern Hemisphere.
  • Plages and Sunspots The chromosphere of the Sun is continuously changing, Bright spots on the chromosphere are called Plages and dark spots are called Sunspots. The Sunspots are cold and dark regions on the Sun’s surface with a periodicity of 11 years. These spots greatly influence the global climate.


Planets are celestial bodies, which continuously revolve around and are lighted by a star. They have sufficient mass and self-gravity to overcome rigid body forces such that they assume a hydrostatic equilibrium shape. There are eight planets in the solar system that revolve around the Sun in an elliptical order, listed according to their distance from the Sun as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

The sequence of planets according to their size (in descending order) is Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, and Mercury.

A dwarf planet is a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape, and has not cleared the neighborhood around its orbit.

Classification of Planets

  1. Inner Planets include Mercury, Venus, Earth and Mars. They are known as Terrestial or Rock planets and are nearer to the Sun having very few natural satellites. They have a core of molten rocks and they move faster taking shorter period of revolution.
  2. Outer Planets include Jupiter, Saturn, Uranus and Neptune. They are known as Jovian or Gaseous planets and are far away from the Sun having a large number of natural satellites. They are formed mainly of gases, with a small rocky core and they move rather slowly taking a longer period of revolution.

Planets Fact Sheet

Biggest PlanetJupiter
Biggest SatelliteGanymede (Jupiter)
Blue PlanetEarth
Green PlanetUranus
Brightest PlanetVenus
Brightest Star Outside Solar SystemSirius (Dog Star)
Closest Star of Solar SystemProxima Centauri
Coldest PlanetNeptune
Evening StarVenus
Farthest Planet from SunNeptune
Planet with maximum number of satellitesSaturn
Fastest Revolution in Solar SystemMercury
Densest PlanetEarth
Fastest Rotation in Solar SystemJupiter
Morning StarVenus
Nearest Planet to EarthVenus
Nearest Planet to SunMercury
Red PlanetMars
Slowest Revolution in Solar SystemVenus
Slowest Rotation in Solar SystemVenus
Smallest PlanetMercury
Smallest Natural SatelliteDeimos
Earth’s TwinVenus
Only Satellite with an Atmosphere like EarthTitan
Hottest PlanetVenus
Fact Sheet

Pluto–Out of Orbit!!

Pluto lost the coveted honor of being a planet and is demoted to being a dwarf planet. It was discovered by Clyde Tombaugh in 1930. It has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.

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The moon is the only Earth’s natural satellite. The study of the Moon is called Selenology. It is also known as a fossil planet. It has no atmosphere and no twilight.

The size of the Moon is one-fourth (1/4th) the size of the Earth. The gravitational pull of the Moon is one-sixth (1/6th) that of the Earth. The majorly found elements on the Moon’s surface are silicon, magnesium, iron, etc.

Specifics of the Moon

Distance from Earth384400 km
Mass (with respect to Earth)1: 81
Diameter3475 km
Ratio of Gravitational Pull of Moon and Earth1: 6
Highest Mountain18046 ft
(Hugyens Mountain)
Time taken by moonlight to reach Earth1.3 s
Rotation speed3680 km/h
Speed of Revolution around Earth3680 km/h
Revolution Period around Earth27 days, 7 h, 43 min, and 11.47 s
Rotation Period27 day, 7 h, 43 min, and 11.47 s
Part of Moon not visible from earth41%
Maximum distance from earth (Apogee)406000 km
Minimum distance from Earth (Perigee)356400 km
Circumference11000 km

Interstellar Debris:


Asteroids are bits and pieces composed of rocks, dust, and metal, left behind when our solar system was made. They have no definite shape and size and are also called planetoids or minor/small planets. They orbit around the Sun in the asteroid belt, which lies between the orbits of Mars and Jupiter. This belt stretches from about 250 million to 600 million km from the sun.


Meteoroids are small fragments of rocks and metal smaller than comets. They are tiny lumps of burning matter and streak through the solar system. Those meteors that enter the earth’s atmosphere are called meteors and those that crash upon the earth are called meteorites. Under the Earth’s gravitational field, they burn and become white-hot through friction as they fall through the atmosphere and are seen as Meteors or Shooting stars. They don’t have any definite shape and they travel through space. Meteors are scattered in the interplanetary space of the solar system.


Comets are icy, rocky masses that have a solid nucleus surrounded by a cloud of glowing gases called the coma. It may originate in a huge cloud called the Oort cloud that surrounds the solar system. They have glowing tails pointing away from the sun because of the solar wind and the radiation pressure. They have an extremely eccentric orbit but with definite periodicity.

Do practice logical reasoning sheets: SYLLOGISM Practice Questions with solutions | Blood Relation | Consanguinity: Solved Examples with Diagrams

Who was the second man to land on the moon?

Edwin Aldrin was the second man after Neil Armstrong to land on the moon.

To which galaxy does the solar system belong?

Our solar system belongs to the Akash Ganga or the Milky Way.

What is a light-year?

The distance that light travels in a year is called a light-year.

What are sunspots?

Sun Spots are areas of the sun that are slightly less hot. They appear as barrier spots on the otherwise shining sun which are not stationary.

What are Small Solar System Bodies?

All the objects orbiting the Sun shall be referred to collectively as ‘Small Solar System Bodies’.

In which direction do planets move?

Planets move around the sun in an anti-clockwise direction, i.e, west to east.

How long does Mercury take to complete one revolution?

Mercury takes 88 days to complete one revolution.

Which is India’s satellite launch base?

Sriharikota Island has been developed by India as a launch base with the most modern launch infrastructure for satellite launching.

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Arpita Choudhary
Arpita Choudhary
Passionate for writing, enjoy writing on variety of topics and I take pleasure in immersing myself in learning about new and exciting domains.

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