Tuesday, November 29, 2011

Origin of Asteroids

Asteroids are believed to have originated during the formation of the Solar System, when planetesimals accreted from solar nebula. The more primitive carbonaceous asteroids may have evolved little since then, while the other types may have been parts of larger bodies that first accreted and later broke up by collisions.

Recently a few small asteroids have been discovered in highly elliptical orbits that come inside the orbit of Mars, some crossing the orbit of the Earth - the Apollo, Amor, and Aten families.

Known Asteroids

Today a large number of asteroids are known.Around two thousand of them have well-determined orbits and revolve around the Sun as part of the 'main belt', in the gap between Mars and Jupiter.

They are tiny, only a handful having a diameter of more than a few tens of kilometres, and the combined mass of all the asteroids is thought to be only a fraction of that of the Moon.


Asteroids are the debris of planets that orbit the Sun. These are different sized chunks of rock,ranging from specks of dust to some which are a few hundred kilometres across.

Asteroids follow different orbits.In the eighteenth century, astronomers were convinced that a missing world existed between Mars and Jupiter.A search was mounted and the first asteroid, Ceres, was discovered in 1801.

Sunday, November 27, 2011

Meteors and Meteorites

Meteors are the hot glowing pieces of rocks and dust from space that plunge into the Earth's atmosphere.Most meteors burn up above an altitude of 100km. If u gaze at the stars for half an hour on a clear bight,you will seen an occasional streak of light, which is a meteor's glowing trail.

Orbits of comets

 Orbits of comets

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Comets are believed to be left over particles from beginning of the Solar System,when most of these particles collided with each other to build up the planets. The comet nuclei, containing crumbly rock particles trapped in frozen ice, were left. If their orbits take them near the Sun, the heat turns the outer ice to vapour and solid particles are released as dust. In their frozen state far from the Sun, comets are invisible. Each time a comet passes near the Sun it pours some more of its nucleus into space. Eventually it 'dies' and becomes just an orbiting rock.  

Halley's Comet

Halley's Comet's
Halley's comet is the most famous of all comets, recorded by Chinese astronomers in 467 BC (and possibly in 611 BC). It is a periodic comet orbiting the Sun in a retrograde direction with a period of 76 years. It is named for the English astronomer Edmund Halley, who applied to comets Newton's theory of planetary motions and correctly predicted the return of the bright comet in the year 1758.


Comets are icy objects which travel through the Solar System. A bright comet in the night sky looks like a hazy patch with a long wispy tail. Comets travel in orbits through the Solar System.They evaporate gas and dust and grow long tails when they are near enough to the Sun's heat and light.

The tails always point away from the Sun, blown by the light and streams of atomic particles from the Sun. the most famous comet, Halley's Comets, can be seen from the Earth every 76 years.

The Zodiac

The Zodiac

We cannot see stars during the day because the Sun is too bright, but if we could we would notice the Sun slowly moving through the star patterns. It makes a trip right round the sky once a year, travelling through a band of constellations called the zodiac. The ancient Greeks divided the zodiac into 12 equal zones, called the 'signs' of the zodiac.

Each sign corresponds roughly to one of the zodiac constellations, through the official constellations that astronomers use are not all equal in size. People called astrologers make predictions about people's lives, based on the signs of the zodiac.



Groups of stars that make patterns in certain part of the sky are known as constellations. Some of them were named by the Greeks 2000 years ago, and Arab and Chinese astronomers had their own constellations too. There are 88 constellations and they cover the whole sky. They were probably invented as a way of referring to particular stars. Although the stars in a constellations appear to us to be in group, they are really vast distances away from each other.


Ursa Major


Views of milky way

Views of milky way

The Milky Way is a spiral galaxy with a nucleus of old stars surrounded by halo of much younger stars. the name given to the galaxy is because of its appearance like bright,creamy band of stars stretching across the sky when seen from the Earth.

The Area Of Milky Way

The Area Of Milky Way

The diameter of the Milky Way is around 1,00,000 light years.It circles the whole sky which one can see wherever one is on the Earth. In the North, the constellations 
( groups of stars) it goes through include
 Auriga, Cassiopeia and Cygnus. Dark patches in the Milky Way are actually clouds of dust cutting out the light from the stars. The most famous one, 'the Coalsack', is in the Southern Cross.

Birth Of Stars

Birth Of Stars
Stars are born  and  may  shine  for  thousands  of  millions  of  years  before  they  die. A  cloud  of  gas  and dust  condenses  to form  a  young  star. Some  massive  stars,at the end  of  their  life,explode  as  supernovae  and  could  become  black  holes  or  neutron  stars. Smaller  stars  at  the  end  of  their  life,expand  into  red  giants and  then  shirnk   into  white  dwarfs  that  shine  dimly.

Our Sun and  all the stars you can see in the night sky belong  to a giant family of stars that we call our Galaxy. It contains around 100,000 million stars.This Galaxy is known as the Milky  Way. Beyond our own Galaxy, there are countless other galaxies scattered all across the  space.

Saturday, November 26, 2011

Stars And Galaxies

Stduying Stars

By studying many stars,astronomers have found that they belong to different groups. Some are very hot and shine with bluish light, while others are much cooler and look reddish. These tints can be seen in many of the naked -eye stars that from the constellations. For example, the brightest star in the sky,Sirius,is much whiter and hotter than the Sun, while the closest known star after our Sun, Proxima Centauri, is small, dim and red, the Sun is a medium hot star.

Tuesday, November 1, 2011