The Universe


  • The universe is a huge wide-open space that holds everything from the smallest particle to the biggest galaxy. No one knows just how big the Universe is.
  • Astronomers try to measure it all the time. They use a special instrument called a spectroscope to tell whether an object is moving away from Earth or toward Earth.
  • Based on the information from this instrument, scientists have learned that the universe is still growing outward in every direction. Scientists believe that about 13.7 billion years ago, a powerful explosion called the Big Bang happened.
  • This powerful explosion set the universe into motion and this motion continues today. Scientists are not yet sure if the motion will stop, change direction, or keep going forever.


  • Pythagoras first termed the order of the universe as ‘Cosmos’.
  • The study of Cosmos, that is, the attempt to comprehend the implicit order within the whole of being, is known as Cosmology.

Composition of the Universe

Wilkinson Microwave Anisotropy Probe (WMAP)

  • mission that launched June 2001 to make fundamental measurements of cosmology — the study of the properties of our universe as a whole.
  •  WMAP has been stunningly successful, producing a new Standard Model of Cosmology.
  • It has been successful in measuring the fundamental parameters of the Big Bang model. The measurement included the density and composition of the universe.
  • It accurately calculates the relative density of baryonic and non-baryonic matter better than a few percentage of overall density.
  • The total density can be broken down to be.

Dark Matter and Dark Energy

Cold Dark Matter
  • It is believed that dark matter is made up of one or more kinds of sub-atomic particles.
  • These particles interact with ordinary matter very weakly.
  • Particle physicists see a number of reasonable candidates for the dark matter, and there is a possibility of coming to light many more new particles in near future.
Dark Energy
  • The universe comprises only 4.6% atoms. A much greater fraction, 24% of the universe, is a different kind of matter that has gravity but does not emit any light — called “dark matter”.
  • The biggest fraction of the current composition of the universe, 71%, is a source of anti-gravity (sometimes called “dark energy”) that is driving an acceleration of the expansion of the universe.

Vastness of the Universe

  • The vastness of the universe is clearly beyond normal comprehension. To begin to develop a feel for astronomical distances, we might consider a reduced scale model of the universe.
  •  If the distance between the Earth and the Sun, which is 150000000 km, is taken to be 2.5 cm, then the distance from Earth to the nearest star would be 72 km, and distance from the earth to the next galaxy beyond the Milky Way would become about 40000 km.

Theories of how universe began

  • Nearly 14 billion years ago, there was nothing and nowhere. Then, due to a random fluctuation in a completely empty void, a universe exploded into existence.
  • Something the size of a subatomic particle inflated to unimaginably huge size in a fraction of a second, driven apart by negative-pressure vacuum energy. Scientists call this theory for the origin of the universe the Big Bang.

The Big Bang theory

  • Today, the consensus among scientists, astronomers and cosmologists is that the Universe as we know it was created in a massive explosion that not only created the majority of matter, but the physical laws that govern our ever-expanding cosmos.
  • This is known as The Big Bang Theory. 
  • The basics of the theory are fairly simple. In short, the Big Bang hypothesis states that all of the current and past matter in the Universe came into existence at the same time, roughly 13.8 billion years ago.
  •  At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding and the universe as we know it began.
  • While this is not the only modern theory of how the Universe came into being – for example, there is the Steady State Theory or the Oscillating Universe Theory – it is the most widely accepted and popular. 

The inflation theory

Immediately following to the Big Bang, The universe likely to begin a period of exaggerated outward expansion, with matter flying outward faster than the current speed of the light. This is the inflation theory, widely accepted in the astrophysics community.

The Oscillating Universe theory

  • This theory, a variation of big bangs theory, suggests that the expansion of the universe will eventually slowdown and stops, followed by contraction of the galaxies into another Big bang.
  • The universe therefore continues in endless cycles of expansion and contraction; hence, the laws of the nature may differ in each cycle.

The Steady state theory

  • An alternative view of Big bang theory, this theory says that the universe neither originated at any one instant, nor will it ever die.
  • According to this theory, as the universe expands new matter is created to fill the space left. Therefore, the appearance of the Universe remains constant with time.

Galaxy and the Local Group

  • A galaxy is a huge collection of gas, dust, and billions of stars and their solar systems. A galaxy is held together by gravity. Our galaxy, the Milky Way, also has a super massive black hole in the middle.
  • Perhaps the most conspicuous activity in galaxies occurs in their nuclei, where evidence suggests that in many cases super massive objects—probably black holes—lurk. These central black holes apparently formed several billion years ago; they are now observed forming in galaxies at large distances (and, therefore, because of the time it takes light to travel to Earth, at times in the far distant past) as brilliant objects called quasars.


  • Our Sun (a star) and all the planets around it are part of a galaxy known as the Milky Way Galaxy. A galaxy is a large group of stars, gas, and dust bound together by gravity.
  • They come in a variety of shapes and sizes. The Milky Way is a large barred spiral galaxy. All the stars we see in the night sky are in our own Milky Way Galaxy.
  •  Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area.

Solar System

  • Our solar system consists of our star, the Sun, and everything bound to it by gravity – the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune; dwarf planets such as Pluto; dozens of moons; and millions of asteroids, comets, and meteoroids.
  • Beyond our own solar system, there are more planets than stars in the night sky. So far, we have discovered thousands of planetary systems orbiting other stars in the Milky Way, with more planets being found.
  •  Most of the hundreds of billions of stars in our galaxy are thought to have planets of their own, and the Milky Way is but one of perhaps 100 billion galaxies in the universe.
  • Our solar system extends much farther than the eight planets that orbit the Sun. The solar system also includes the Kuiper Belt that lies past Neptune’s orbit. This is a sparsely occupied ring of icy bodies, almost all smaller than the most popular Kuiper Belt Object – dwarf planet Pluto.


  • A constellation is a group of stars that appears to form a pattern or picture like Orion the Great Hunter, Leo the Lion, or Taurus the Bull.
  • Constellations are easily recognizable patterns that help people orient themselves using the night sky. There are 88 “official” constellations.
  • “Modern” constellations — like the Peacock, Telescope, and Giraffe — were identified by later astronomers of the 1500s, 1600s, and 1700s who used telescopes and who were able to observe the night sky in the southern hemisphere.
  • These scientists “connected” the dimmer stars between the ancient constellations. There are 38 modern constellations.

Cosmology and Cosmic rays

  • Cosmology is a branch of astronomy that involves the origin and evolution of the universe, from the Big Bang to today and on into the future. According to NASA, the definition of cosmology is “the scientific study of the large scale properties of the universe as a whole.
  • Cosmologists puzzle over exotic concepts like string theory, dark matter and dark energy and whether there is one universe or many (sometimes called the multiverse). While other aspects astronomy deals with individual objects and phenomena or collections of objects, cosmology spans the entire universe from birth to death, with a wealth of mysteries at every stage. 
  • Cosmic rays are atom fragments that rain down on the Earth from outside of the solar system. They blaze at the speed of light and have been blamed for electronics problems in satellites and other machinery.
  • Discovered in 1912, many things about cosmic rays remain a mystery more than a century later. One prime example is exactly where they are coming from. Most scientists suspect their origins are related to supernovas (star explosions), but the challenge is that for many years cosmic ray origins appeared uniform to observatories examining the entire sky.


  • Stars are born within the clouds of dust and scattered throughout most galaxies. A familiar example of such as a dust cloud is the Orion Nebula. Turbulence deep within these clouds gives rise to knots with sufficient mass that the gas and dust can begin to collapse under its own gravitational attraction.
  • As the cloud collapses, the material at the center begins to heat up. Known as a protostar, it is this hot core at the heart of the collapsing cloud that will one day become a star.
  • Three-dimensional computer models of star formation predict that the spinning clouds of collapsing gas and dust may break up into two or three blobs; this would explain why the majority the stars in the Milky Way are paired or in groups of multiple stars.

Classification system of Stars

  • Stars are also classified by their spectra (the elements that they absorb). Along with their brightness (apparent magnitude), the spectral class of a star can tell astronomers a lot about it.
  • There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M. O and B are uncommon, very hot and bright. M stars are more common, cooler and dim.
  • This system is referred to as the Morgan Keenan system. The Morgan-Keenan (MK) system is used in modern astronomy a classification system to organize stars according to their spectral type and luminosity class. The system was introduced by William Wilson Morgan and Philip C Keenan in 1943.
  • This diagram shows the typical properties for each type of star. 


  • Main sequence stars over eight solar masses are destined to die in a titanic explosion called a supernova. A supernova is not merely a bigger nova.
  • In a nova, only the star’s surface explodes. In a supernova, the star’s core collapses and then explodes. 

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