• The universe comprises billions of galaxies which
are made up of millions of stars held together by the
force of gravity and these stars account for most of
the masses of the galaxy.
• Our own galaxy is called the Milky Way (or the
Akashganga) and it contains about 300 billion stars
and one of these is our Sun. Planets and other objects
go round the Sun and make up the solar system with
the Sun at the centre.
• In the 14th Century, Ptolemy propounded the theory
that the Earth was the centre of the universe and the
Sun and the other heavenly bodies revolved around it.
• In 1543 AD, Copernicus said that the Sun is the
centre of universe and not the Earth.
• Kepler supported Copernicus but said that the Sun
is the centre of solar system and not the universe.
MEASUREMENT UNITS OF SPACE
• Light Year: It is the distance covered by light in one
year in vacuum at a speed of 300000 km/s. 1 light
year = 9.46 × 1012 km.
• Astronomical Unit (AU): It is the mean distance
between the Earth and The Sun. One Light Year is
equal to 63,000 AU
1 AU = 150 million km.
• Parsec: One parsec is the distance to a star that
subtends an angle of one second of an arc length of 1 AU
1 Parsec = 3.26 light years (3.086 × 1013 km).
ORIGIN: EVOLUTION OF THE UNIVERSE
(I) BIG BANG THEORY
(PROPOSED BY GEORGES LE MAITRE).
• Big Bang was an explosion that occurred 13.8 billion
years ago, leading to the formation of galaxies of stars
and other heavenly bodies.
(II) STEADY STATE THEORY
• Bondi, Gold and Fred Hoyle developed this theory
and states that although the universe is expanding,
it nevertheless does not change its appearance over
time, it has neither beginning nor end.
(III) THE PULSATING THEORY
• According to this theory, the universe is supposed
to be expanding and contracting alternately, i.e.,
pulsating. At present, the universe is expanding.
• Milky Way Galaxy formed 5 billion years
after the Big Bang.
• Latest known galaxy is the Dwarf Galaxy.
• Origin of the universe is explained by the Big Bang
Theory, formulated and proposed by the Belgian
astronomer and cosmologist, Georges Lemaitre.
• Andromeda is our nearest galaxy.
STAR FORMATION
• Stars are made of hot burning gases.
• They emit light o f their own and are very
large and very hot.
• Light takes about 4.3 years to reach us from the next
nearest star Proxima Centauri.
LIFE CYCLE OF A STAR
1. Proto Star: It is the stage, where the helium core
becomes increasingly heavy accompanied by
expanding out the layers. A Proto Star is a highly
condensed cloud of gases mainly hydrogen and
helium.
2. Red Giant: This stage results into the swelling and
reddening of the outer regions of the star. Such
stars of gigantic dimension are called Red Giants.
3. White Dwarf: If the mass of the star is relatively
small like that of our Sun, the gases that reach the
outer layer are expelled. As these expelled gases
cool and contract, the star becomes a white dwarf.
THE SOLAR SYSTEM
• The Sun, eight planets (excluding Pluto) and their
respective satellites.
• Interstellar debris such as asteroids, meteoroids, comets.
• The electrically charged gases, called Plasma.
• Interplanetary dust particles.
• The components of solar system other than planets,
dwarf planets and satellites are called the Small Solar
System Bodies (SSSB).
• The gravitational pull of the Sun keeps all the planets
and other objects revolving around it.
• Planets revolve around the Sun in an elliptical orbit.
• In the solar system, the planet nearest to the Sun
is Mercury and the planet farthest from the Sun is
Neptune (not Pluto).
• The solar system is dominated by the Sun, which
accounts for almost 99.9% of the matter in the
whole solar system.
• Pluto is a dwarf planet.
• Mercury, Venus, Earth and Mars are called
terrestrial planets and Jupiter, Saturn, Uranus and
Neptune are called gaseous planets.
MEMBERS OF THE SOLAR SYSTEM
THE SUN
• It is the nearest star to the Earth.
• Its diameter is 14 lakh kms.
• It is composed of 71% hydrogen, 26.5% helium and
2.5% other elements.
• Within the Sun, hydrogen is converted to helium due
to nuclear fusion releasing a tremendous amount of
heat and light.
• The shining surface of the Sun is called
Photosphere.
• The outer layer of Sun’s atmosphere made up of thin
hot gases is called Corona.
• The middle surface is chromosphere. The temperature
of Photosphere is 6000°C, that of chromosphere about
32400°C and that of Corona about 2700000°C.
• The planet travels with the Sun through millions of stars
in our galaxy at a speed of about 70,000 kms per hour.
• The Sun is about 150 million kms away from the Earth.
• Light takes about 8 minutes 20 seconds to reach the
Earth from the Sun.
• Solar Winds: The Sun is continuously emitting
streams of proton in all directions either as spiral
streams called Solar Wind or bouts of incandescent
material called Solar Flares. Solar flares, being hot
ionised gases, pose danger to satellite communication.
• Aurora: The constituent particles of the solar wind are
trapped by the Earth’s magnetic field and enter the
Earth’s upper atmosphere as Aurora. It is described
as Aurora Borealis in the Northern hemisphere and
Aurora Australia in Southern hemisphere.
• Bright spots are called Plages and dark spots are
called Sunspots.
Tags:
General knowledge