Our Universe and the Solar System
Posted on : 28-01-2019 Posted by : Admin

Introduction

Solar system is the group of celestial bodies with sun at its centre. It comprises of eight planets namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. All these planets revolve round the sun. Many satellites revolve round their respective planets. The solar system also includes thousands of comets, millions of asteroids, billions of meteoroids and huge quantity of dust-grains and gases.

The planets move around the sun, this motion is called revolution. Each planet also spins around an internal axis, this motion is called rotation.

Order of the planets (nearest first) MVEMJSUN

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Order of contents of solar system (decreasing order in numbers)

dust-grains and gases, Meteoroids, Asteroids, Comets, satellites, Planets

Pluto is no more a Planet

The definition of a planet was revised in August 2006, by International Astronomical Union. As per this new definition, a planet is a celestial body that,

  1. Is in orbit around the sun;
  2. Has sufficient mass for its self gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape;
  3. Has cleared the neighborhood around it orbit.

According to this new definition, Pluto does not satisfy the third point. The orbit of Pluto is most elliptical, and as a result, it intersects the orbit of Neptune. In its journey round the Sun, Pluto for some years comes closer to Sun than Neptune. Therefore, Pluto has been excluded from the category of planets and is included into the list of Dwarf planets.

After being demoted from planet status, Pluto again got a consolation prize in the year 2008, when International Astronomical Union decided that Pluto and other dwarf planets like it will be called Plutoids.

Plutoids are the celestial bodies in orbit around the sun at a distance greater than that of Neptune, that have sufficient mass for their self gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium shape. But that have not cleared the neighborhood around their orbit. To known and named plutoids are Pluto and Eris.

 

Important points about Planets

  1. All the planets were formed in same period about 4.6 billion years ago.
  2. All the planets rotate upon their axis in anti-clockwise direction (west to east). The exceptions are Uranus and Venus which rotate upon their axis in clockwise direction (east to west).
  3. For all the planets, the direction of revolution around the sun is in anti-clockwise direction (west to east)
  4. Planets have no light of their own. They get their light from the sun.
  5. Satellites revolve round the planets. For example, Earth has 1 satellite; Jupiter has about 60 satellites while Mercury and Venus have no satellites.
  6. Very small planets or the fragments of planets revolving round the sun between the orbits of Mars and Jupiter are called Asteroids or Planetoids.
  7. Out of eight planets, the planet nearest to earth is Venus. Mercury and Venus which are closer to sun than Earth are called inferior planets. All the other planets which are at greater distance are called superior planets.
  8. As per another way of grouping Mercury, Venus, Earth and Mars are called Inner planets as they lie between Sun and the belt of asteroids. The other four planets are called outer planets.
  9. Yet another way of grouping, groups Mercury, Venus, Earth and Mars as Terrestrial planets. Terrestrial meaning earth-like, as they are made-up of metals and rock. Terrestrial planets have high density. The remaining four planets are called as Jovian planets. Jovian meaning Jupiter-like, with thick atmosphere made up of helium and hydrogen.
MERCURY
  • It is smallest planet of the solar system.
  • It is nearest planet to Sun.
  • It has no atmosphere and no satellites.
  • Its days are scorching and nights are freezing.
VENUS
  • It is brightest planet of the solar system.
  • It is nearest planet to Earth.
  • It is probably the hottest planet. Both the day and night temperatures are same.
  • Its atmosphere consists of 90-95% carbon dioxide. And Green house effect is prominent here.
  • It is Atmospheric pressure is 100 times that of the Earth.
  • Due to its similarity with the Earth with respect to size and mass, it is called Earth’s twin.
EARTH
  • It is Fifth largest planet of the solar system.
  • It is most massive and dense of all the four terrestrial planets.
  • It is also called the World, the Blue planet or Terra.
  • It is the only planet where the life exists. It is home to millions of species.
  • It has only one satellite, Moon
MARS
  • It is a shining planet, with two satellites Phobos and Demos.
  • It has thin atmosphere consisting of nitrogen and Argon.
  • It has dormant volcanoes, deep chasms where water flowed once.
  • The highest mountain present here is named Nix Olympia, which is three times higher than Mt. Everest.
  • It is called Red planet.
  • Recent explorations revealed occurrence of ice caps and frozen water. Hence, a ray of hope for the existence of life here.
JUPITER
  • It is largest planet of the solar system.
  • Its atmosphere consists of hydrogen, helium, Methane and ammonia
  • It reflects more than three times the energy it receives from Sun.
  • It has a great red spot which is an enormous whirlpool in the turbulent cloud cover.
  • It also contains dusty rings and volcanoes
SATURN
  • Saturn is the sixth planet from the Sun
  • It is the second largest planet in our solar system.
  • It is a massive ball made mostly of hydrogen and helium.
  • It consists of thousands of beautiful ringlets. WIth these rings it appears is unique among the planets. It is not the only planet to have rings through.
  • The rings of saturn are made up of chunks of ice and rock
URANUS
  • This plant has 9 dark compact rings around it and a corkscrew magnetic field that stretched for millions of miles.
  • Its atmosphere consists mainly of Methane.
  • It is only planet in the solar system here one pole or other faces the sun as its orbit.
  • It has 15 satellites
NEPTUNE
  • Neptune consists of five rings around it.
  • The outer ring is studded with icy moonlets while the inner ring appears narrow and nearly solid.
  • It has 8 satellites
  • It is the only planet in the solar system which is not visible to naked eye
  • It is the farthest planet from the sun
  • The atmosphere of Neptune has poisonous gases like methane and ammonia.

Other Important inclusions of the solar system

Asteroids: Asteroids are also called as planetoids. These are a series of small planets or the fragments of the planets which lie between the orbits of Mars and Jupiter. Their number is about 45,000. The largest asteroid is Ceres with length of about 1000 km. Asteroids revolve round the sun in the same manner as the planets.

Comets: The name comet is derived from Latin words Stella cometa meaning “hairy star”. These are the most beautiful and unpredictable bodies in the solar system. It is believed that comets are formed for the remaining material left after the formation of outer planets. They are composed of frozen gases held together by rocky and metallic material. Generally a comet consists of three parts namely Centre, coma and tail

  • Centre-Consists of dusty particles
  • Coma- it is the part connecting the centre with the ail
  • Tail- It arises only when the comet comes close to the sun. The tail of the comet is always directed away from the sun because lighter mass of the comet is pushed away due to centrifugal force as the comet comes close to the sun.

Though hundreds of comets pass through the inner solar system, only a few are notices by the casual observers. About every decade or so, a comet will become bright enough to be noticed. Such comets are called greater comets.

Meteors: These are the pieces of matter which have entered the Earth’s atmosphere from the outer space, due to the gravitational pull of the Earth when they are passing close to the earth. Meteors are probably the remnants of the 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 burn completely in to ash are called meteors.

Meteorites: Meteors and meteorites are called as shooting stars. Meteors which are large, do not burn completely and strike the Earth in the form of rocks are called meteorites. Meteorites are believed to originate in the asteroid belt.

Stars: These are heavenly bodies made up of burning gases and thus have the light of their own. They are in fixed positions with respect to each other. Though they are in rapid motion, the relative changes cannot be felt immediately due the great distance between them.

The closest star to the Earth after Sun is Proxima Centuari. Other examples of stars include Polaris, Sirius, Vega, Capella, Spica etc.

Constellations: Constellations are man-made divisions in the sky, to enable the astronomers identify the rough position of the stars. These constellations are names in honor of the mythological characters. Currently 88 constellations are recognized.

Constellation Indian name
Ursa Major (great bear) Saptarishi
Ursa Minor Druva Matsya
Orion Mriga
Draco Kaleya
Scorpion Vrischika
Aries Mesha
Taurus Vishabha
Gemini Mithuna
Cancer Karataka
Leo Simha
Virgo Kanya
Libra Tula
Sagittarius Dhanur
Capricorn Makara
Aquarius Kumbha
Pisces Meena

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