Universe means unimaginably vast space
which is unbounded with its dots of body's are by definition, the universe
includes everything that abounds in space, and space is filled with matter
which varies from the tiniest and cosmic particle to the gigantic galaxies. The
universe is known to composed of many types of comparatively small and large
dense Bo e.g., the galaxies, the constellations (star groups), the stars, the
planets other heavenly bodies.
The totality of the heavenly
bodies from grand galaxies down to the sm cosmic dust filling the endless space
describes the Universe w dimension is beyond our comprehension.
There are t divergent theories on
the mode of origin of the universe. These are the B Bang and the Steady State
theories. According to 'Big Bang' theory universe has a finite beginning,
through a tremendous explosive expansion superdense and very condensed matter.
The "steady state" theory states the universe expands through a
process of continuous creation of matt which (the process) remains unchanged
through eternity.
Galaxy: A galaxy is a rotating
stellar system (star system) consisting of a swarm of stars which are held
together by mutual gravitational attraction. In other words, a galaxy is an
enormously large cluster of stars. Our galaxy to which the sun along with its
planet families belong is an aggregate of aboii one hundred billion stars. Ours
is called "Milky way" galaxy which looks like a discuss (a
disc-shaped metal used in discus throw) when viewed through powerful optical
telescope.
It is a pancake shaped whirling
body which is gigantic in size. A part of the "Milky way" is clearly
seen with naked eye as a faint luminous broad band across the sky during a
clear autumn night. It takes about 100,000 years for the light to go from one
end of our galaxy to the other end. There are billions of galaxies in the
universe. The nearest galaxy comparable to our Milky Way in size is the
Andromeda galaxy.
Stars and Planets: A star is a
self-luminous and incandescent globe of hot gases. Stars produce their own
light and are seen twinkling in the sky. The stars vary in size, temperature
and constituent materials. Many stars occur in pairs (twins). They may even
occur in triplets or quadruplets.
Most of the stars have their own
systems of planets and satellites revolving round them. In such cases, a star
constitutes a star system. Our sun is a star having its own planetary and
satellite system called the "solar system".
Planets and satellites are
non-luminous heavenly bodies which shine only because of reflection of star
(sun) light from their surface. The planets whirl round their stars in definite
orbits.