Existing matter and energy are together
known as universe. The study of universe is known as Cosmology. Universe
includes all the universal bodies and the complete solar family which comprises
the sun, moon, planets, comets, planetoids etc.
Origin of the universe is explained by the
Big Bang Theory, which was formulated and proposed by the Belgian astronomer and
cosmologist Georges Lemaitre, after his becoming acquainted with the findings
of the American astronomers Edwin P. Hubble and Harlow Shapley on the expanding
universe.
Main points of the Big Bang Theory:
·
All the matter in the universe was
originally one concentrated lump called primeval atom.
·
Big Bang was an explosion that occurred 15 billion
years ago, leading to the formation of galaxies of stars and other heavenly
bodies.
·
Since then, all the galaxies have been
flying away from one another causing expansion of the universe.
Galaxy
A large group of stars, dust and light
gases, bound together by their own gravity is called a galaxy. It contain billions of stars, which also contains a
large number of gas clouds (mainly of hydrogen gas) and dust, isolated in space
from similar systems.
·
There are about 100 billion galaxies in the
universe, and each galaxy has, on an average, 100 billion stars.
·
The Milky Way Galaxy is the home of the
Earth and our Solar System. It is spiral in shape.
·
Latest known galaxy is the Dwarf Galaxy.
·
We live on the outer edge of a spiral type
of galaxy called the Milky Way, which is about 100,000 light years in diameter
and is rotating slowly.
Main points of the Earth’s Galaxy: The Milky Way
·
The Milky Way is a large spiral-shaped
galaxy.
·
It is called the Milky Way because it
appears as a soft glowing light of billions of stars. These stars are so far
that they can be seen only in constellation; not separately.
·
Galileo discovered that this band of light
was produced by countless individual stars which a naked eye cannot see.
·
It takes about 250 million years to complete
one revolution.
Main points of the Andromeda: Earth’s closest Galactic
neighbour
·
Andromeda is a spiral galaxy and also our
closest neighbour.
·
It is the farthest object that can be seen
with the naked eye.
·
Like stars, galaxies are grouped into
clusters. Some clusters contain thousands of galaxies.
·
About 30 galaxies, along with the Milky Way
and the Andromeda are grouped together in one cluster called the Local Group.
Nebulae
·
Nebulae are huge interstellar clouds of gas
and dust that appear as faint, misty patches of light scattered all over the
sky.
·
They appear either as bright luminous clouds
or as dark patches against a brighter background.
·
A nebula depends for its luminosity upon the
presence of stars that have either arisen from it or are contained in it.
STARS
·
Clumps of dust and gas in a nebula come
together due to their own gravity and form stars.Stars are made of hot burning
gases. They emit light of their own. They are very large and very hot.
·
Stars seem to be fixed with respect to each
other. In fact they are in rapid motion but they are at such great distance
that relative changes in position become noticeable only over the centuries.
The star Alpha Centaury (also called Proxima
Centauri) is the closest star to the Earth after the Sun. It is about 4.3 light
years away
