Short Notes about Universe, Galaxy, Stars and Constellations

Astronomy is a science that asks fundamental questions about the very basic of things, the universe. The Universe is all of time and space and its contents. The Universe includes planets, stars galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy. The observable universe is about 28 billion parsecs (91 billion light-years) in diameter at the present time. The size of the whole Universe is not known and may be either finite or infinite. Observations and the development of physical theories have led to inferences about the composition and evolution of the Universe.

What is Universe? 

Everything that exists, from the Galactic Megaclusters to the tiniest subatomic particles, comprises the Universe.

  • As for the age of Universe, scientists agree that it is about 13.79 billion years old as 2015.
  • The universe comprises of a number of galaxies.
  • Optical and radio telescope studies indicate the existence of about 100 billion galaxies in the visible universe.
  • The Big Bang Theory is most accepted for the origin of Universe in comparison to the Steady State and the Pulsating Universe Theory.

What is Galaxy?

Galaxy is a collection of millions or billions of stars and planets that are held together by gravitational pull.

  • Milky Way is one such galaxy. The earth lies in this galaxy. It is called Milky Way, because it looks like a river of milky light flowing from one corner to another of the sky.
  • It is spiral in shape. We call it Akash Ganga.
  • The nearest galaxy to Milky Way is Andromeda. Andromeda is a spiral galaxy and approximately 2.5 million light-years from the earth.

What is a Star?

Luminous heavenly bodies which have their own light and other radiant energy are called star. They are made of extremely hot burning gases.

Star reflects Looks – Red with low temperature, Yellow with higher and blue with very high temperature.

Star (Birth to Death)

  • Star starts its life as clouds of dust and gas known as Nebula.
  • The gaseous matter of Nebula further contracts to make dense region named Proto Star.
  • The Proto Star further condenses to a critical stage of mass where nuclear fusion begins and star finally comes into existence.
  • When all the hydrogens of a star are used up then its helium begins fusing into carbon. At a stage helium’s fusion and energy production inside the star stops. As a result stars core contracts under its own weight to a very high density to make a white Dwarf star.
  • White Dwarf star becomes dark balls of matter on cooling to make Black Dwarf Star.
  • The mass of white Dwarf Star is less than 1.44 times the mass of the Sun named as Chandrasekhar Limiting Mass.
  • White Dwarf Star is a dead star because of the end of fusion reaction and energy production. It shines by radiating its stored heat.
  • Giant star expands into Red Supergiant after consuming its fuel (H & He). At a stage, it explodes as Supernova or changes into Neutron or Black Holes.
  • The nearest star to the Earth is the Sun followed by Proxima and Alpha Centauri and radiant energy. (4.35 light years)


  • A Constellation is a group of stars that makes an imaginary shape in the sky at night.
  • It helps in navigation of sea vessel during night as they are seen in a fixed direction at a particular period of time in a year.
  • Orian, Big Dipper, Great Bear, Cassiopeia are some examples of constellations. • Orion or Mriga can be seen in the late evening during winter; Cassiopeia in the Northern Sky is seen during winter.
  • Great Bear consists of Ussa Minor (Laghu Saptarishi) and Ussa Major (Vrihat Saptarishi), and can be seen in early night during summer.


layers of the sun

  • It is a star made up of extremely hot gases, particularly by hydrogen (70%), Helium (26.5%) and others (3.5%) gases.
  • It is 109 times bigger than the earth and weighs 2 × 1027 tonnes, and accounts for 99.83% of mass of the solar system.
  • It is 150 million km away from the earth. The sun light takes 8 minutes to reach the earth’s surface.
  • It has immense gravitational pull which keeps the planets fixed in their orbit, revolving round the sun.
  • It continuously gives off energy in the form of visible light, infra red, ultra violet, X-rays, gamma rays, radio waves and plasma gas.
  • The period of revolution of the sun around the galactic centre is 250 million year. This period is called as cosmic or galactic year.
  • Sudden flash of brightness observed near the sun’s surface which is a collection of magnetic energy including electrons, protons and nuclei is called as solar flares. They are consized particles and are harmful for satellite communication.
  • The layers of sun are divided according to their brightness level which is represented in the write features of each layer shown in the figure.
  • The core of the sun consists of hydrogen atoms which fuse together due to compression and creates helium. This is called as nuclear fusion.
  • Nuclear fusion produces huge amount of energy. It is radiated outward to the surface, atmosphere and beyond.
  • Convection zone is the next to the core of the sun. Here the temperature drops to 2 million degree C.
  • Photosphere’s temperature is 6,000°C.
  • Atmosphere of the sun consists of chromosphere and corona.
  • Corona is seen in a form of spectral lines emitted by iron, calcium and nickle ions. Ionization of these elements increases temperature of corona.
  • Recently coronal heating puzzle has been related to magnetic carpet found in corona.
  • The solar flare (wind) is a stream of charged particles released from upper atmosphere of the sun. These changed particles when get trapped by earth’s magnetic field while entering in the upper atmosphere of the earth results in auroral (light) display.
  • These auroral display in the northern hemisphere is called as Aurora Borealis (the Northern light) and when occurs in southern hemisphere is called as Aurora Australis (the Southern lights)
  • Sun-spots are dark appearing areas present in photosphere from where solar flares originate . They are relatively a region cooler than its surrounding. It appears and disappears after every 11 years. This period is called Sunspot Cycle.
  • Plage is a brighter region in the chromosphere near to sunspot.

So we hope you liked our post and came to know about Universe, Galaxy, Stars and Constellations. If you want more information. Kindly visit this link > GEOGRAPHY

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