What is a "white dwarf"?

When the nuclear fuel of a star ends up then the gravitational compression leaves the core composed of protons with electron flying around forming a gas- like phase - the electron gas. This electron gas can withstand the inward gravitational force and or stable, equilibrium would be achieved. Such a star is called a white dwarf.

What is a "black dwarf"?

A white dwarf gradually cools , ceases to be self luminous and ends up as a black dwarf.

What is chandrashekhar's limit?

As per S. Chandrashekhar, only those stars end up as a black dwarf whose core mass is up to 1.4 Ms ( Ms is the mass of the sun. )This is known as chandrashekhar limit.

What is a 'neutron star' ?

The star whose core mass lies in between 1.4 M4 and 5 Ms, ends up as a ' 'neutron star.' Due to excess gravitational compression, electrons are forced in to the nuclei; known as inverse beta decay. Such a neutral star is known as " neutron star " The stellar matter is of nuclear density.

What is 'supernova' ?

During the formation of a neutron star by the contraction of the central part of the star, enormous amount of gravitational energy is released. Because of this energy release the outer layers of the star explode. the star's Brightness increases sharply for sometime and then diminishes. this phenomenon is known as the " supernova ."

What is a ' black hole'?

When the core mass of a star is beyond 5 Ms, due to catastrophic gravitational contraction, the core density becomes such high that even light photons can not escape from this region. Hence this is known as 'black hole' The radius of a black - hole, rBH = 2GM/c2, where M is the core - mass.

What is approx diameter of our milky way?

Our sun is situated at a distance of two-third radius of our milky way.

What are thicknesses of the milky way at the centre at solar neighbour hood?

At the centre, it is 5000 light years, while at solar neighbourhood it is 1000 light years.

What is approx mass of our milky way?

It is about 3 ×1041 kg. = 150 billion solar masses.

What is hubble's law and ' BIG BANG THEORY' ?

U = Hr, where U = recession speed of a galaxy for us. r = distance of the galaxy from us. 1/H @ 10 - 20 billion years ( Hubble's Constant. ) BIG BANG THEORY: Initially all matter and radiation were compressed into a fiery region with extremely high temperature and immense, densities, known as the ' primordial fireball. A great explosion launched the expansion of the universe, Known as the 'BIG BANG'.

What is geocentric model of the UNIVERSE?

The earth is stationary and all celestial objects revolve round it. Each planet goes round in a small circle ( epicycle ), the centre of which follows a circular path round the earth. Suggested by greek astronomer Ptolemy in the first century A.D.

What is heliocentric model of the UNIVERSE?

The sun is at rest and the planets revolve round it, proposed by Copernicus in the fifteenth century A.D.

What are the atmosphere's details around various planets?

Venus and Mars - carbon dioxide. ( CO2 ) Jupiter and Saturn - H2, He, CH4, NH3 Uranus and Neptune - H2, He, CH4 Mercury - NIL Pluto - not known properly. Earth - Air

Name the terrestrial planets.

Mercury, Venus, Earth and Mars ( Pluto is also sometime included ). these are relatively small, dense and are probably made of rocks and metallic material.

Name the Jovian planets.

These are Jupiter, Saturn, Uranus and Neptune. These are comparatively large, low in density and are predominantly composed of H2 and He.

What are the comets?

These are composed of frozen gases with nuclei of solid particles. they move around the sun in highly elongated elliptical orbits, spending most of the time far away from the sun. Heads of comets are 10000 - 20000 km in size, the tails can stretch to millions of kilometers. the mass of a comet is exceedingly small, about a billionth that of the earth. comets' that is always oriented away from the sun due to radiation pressure and solar wind.

What are asteroids?

These are minute planets most of whom are only a few kilometers across. Most of them are cofined to the space between the orbits of Mars and Jupiter.

What are meteoroids?

Minute objects orbiting the sun, meteoroids are too small to be observed even with telescopes, when they enter earth's atmosphere, they become visible due to burning & then they are known as ' meteors' or shooting stars.' Sometime they land on the earth's surface and then they are known as ' meteorites.'

Who is zero 'magnitude' star?

'VEGA' star is of zero magnitude and its brightness is lb = 2.52´10-8 Wm-2   brighter stars than VEGA have negative magnitudes.

What are the magnitudes of brightness of various stars? and also limits of minimum brightness to be observed by various instruments?

Sun -26.5 Full moon -12.5 Venus -4.0 Jupiter, mars -2.0 Sirius -1.5 Aldebaran, Altair 1.0 Naked-eye limit 6.5 Binocular limit 9.0 20 cm telescope limit 14.0 5 meter telescope 20.0 5 meter telescope ( visual ) 5 metre telescope ( photo ) 24.