How and What

Astronomical Unit Astronomical unit is the unit of length which is used by astronomers to measure shorter distances or sizes of terrestrial bodies in space. For extremely long distances we use light years but for defining distances comparable to the size of our solar system, we need a unit which is smaller than a light year but much bigger than kilometers. Its symbol is ‘ au ’. For solving this purpose International Astronomical Union defined one astronomical unit as the length in 1976, for which the value of Gaussian Gravitational Constant becomes 0.01720209895 . This is the value when astronomical units of length and mass are used for measurement. Another definition is that the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with an angular velocity of 0.01720209895 radians per day is called one astronomical unit. One more definition is that when we are to describe the position of an object in the solar system,...

Supernova Supernova is an enormous explosion which is caused when either a dead star collapses due to its own gravity or due to collision of two massive black holes. These super powerful explosions are so bright that they can over shine even an entire galaxy and its light can be seen for months. These are one of the most powerful cosmic activities and radiate more energy than the entire energy radiated by a star in its whole lifespan. The life of the luster caused by a supernova is very small as compared to the life of a star. A supernova explosion is the reason for the enormous gamma ray bursts which shoots out tiny particles and harmful electromagnetic waves, most of which is gamma ray. There are various postulates and theories about supernova explosion, some of which are formation of neutron stars, preon stars, boson stars, strange stars and electroweak stars. These hypothetical stars have been described mainly to solve various equations of general relativity. In some c...

Red Giant Red giants are the ending stages of a star which has exhausted all its hydrogen at its core and has started to consume the hydrogen from its outer shell. Only the stars with smaller mass i.e. 0.3 to 8 solar masses become red giant at the end of its life. When the hydrogen in the inner core of the star is fully consumed then the nuclear fusion reaction starts shifting in the outer shells. When the outermost shells of the star start burning, then the core contracts due to its own gravity. This creates an empty space between the core and the outer shell. The outer shell of the star keeps expanding. This expansion is so massive that its radius becomes 100 times bigger than the radius of our sun. Though the core doesn’t burn, even then it is hotter than the expanding shell. The outer shell radiates lesser energy than our sun still it is much brighter because of its extra-large size. The surface temperature of this outer envelope is low, that is why it appears reddish oran...

Nebula An interstellar cloud of dust, hydrogen, helium and other ionized gases is called nebula. Basically nebula was the designation for any diffuse astronomical object, including galaxies other than Milky Way. A nebula may be formed either by supernova explosion when the gases released by the explosion are diffused by the low frequency electromagnetic radiations caused due to the explosions. These diffused ionized gases illuminate under the visible wavelength. Another type of nebula is formed when gases collapse under their own gravitational pull. A massive star is formed at the center and its radiation causes the surrounding  gases  to shine.  In easy language, a nebula is a huge collection of dust and gas in the free space. It is bound together due to its own gravity and has a fading luster. Nebula forms very beautiful shapes and colors in the space. Related Articles:  Astronomical Unit ,  Supernova ,  Red Giant ,  Exotic Star...

Black hole A black hole is a heavenly body with highest possible density and it attracts the other bodies of the universe towards itself with the strongest gravitational pull, capable of even trapping the light. A black hole is not a hole in reality, but a massive body which contains the mass of millions of stars in it. It is shrunk into a very small volume as compared to its mass and if we scratch out 1 cm 3 of matter from its periphery then it would have mass equal of many tons. This unimaginable density of black hole is the result of its extremely high mass causing its compression up to such limits in the effect of the gravity caused by its mass. Many would ask that why did it not shrink when it was a burning star since it had a very high mass at that time too, well it did't because at that time, it was a burning star which lights up because of nuclear fusion reaction inside it causing an outward thrust and thus resisting compression. A black hole forms when a very massi...

White Dwarf A white dwarf is a dead star of comparatively lower mass i.e. approximately 1.3 to 8 solar masses that has all its solar fuel after burning for millions of years and now is in a constant process of cooling. Its color appears white because of the heat radiated from its surface. When a star has consumed all its hydrogen then combustion stops. Since nuclear fusion inside the core of the star stops therefore, the outward pressure due to this combustion declines and star starts compacting due to the enormous gravity produced by its mass. Star heats up more due to this and the rest of the hydrogen also burns in the outer layer of the star causing the outermost layer to expand. This expansion is so massive that it can eat a whole solar system comparable to that of the size of our solar system. This stage of a star is called red giant stage. Due to its large size, the surface is cooler than its core. The core of this red giant is completely made of helium which has be...