The Big Bang is the prevailing cosmological theory of
the early development of the universe. Cosmologists
use the term Big Bang to refer to the idea that the
universe was originally extremely hot and dense at
some finite time in the past and has since cooled by
expanding to the present diluted state and continues
to expand today.
The Solar System consists of the Sun and those celestial
objects bound to it by gravity, all of which were formed
from the collapse of a giant molecular cloud
approximately 4.6 billion years ago.
Of the many objects that orbit the Sun, most of the mass
is contained within eight relatively solitary planets whose
orbits are almost circular and lie within a nearly flat disc
called the ecliptic plane.
The four smaller inner planets, Mercury, Venus, Earth and
Mars, also called the terrestrial planets, are primarily
composed of rock and metal. The four outer
planets, Jupiter, Saturn, Uranus and Neptune, also called
the gas giants, are composed largely of hydrogen and
helium and are far more massive than the terrestrials..
‘SUN’ the Star
• The Sun is the star at the center of the Solar System and is about 109
times larger than the Earth. The Sun's color is white, although from the
surface of the Earth it may appear yellow because of atmospheric
scattering and is mainly composed of helium and hydrogen.
• As the Sun exists in a plasmatic state and is not solid, it rotates faster at
its equator than at its poles whereas if planets are considered they
rotate faster at their poles. After trillions of years stars turn into Red
• Red giants are stars with radii tens to hundreds of times larger than that
of the Sun which have exhausted the supply of hydrogen in their cores
and switched to fusing hydrogen in a shell outside the core.
• A planet is a celestial body orbiting a star or stellar remnant that is
massive enough to be rounded by its own gravity.
• The term planet is ancient, with ties to
history, science, mythology, and religion. The planets were originally
seen by many early cultures as divine, or as emissaries of the gods. As
scientific knowledge advanced, human perception of the planets
changed, incorporating a number of disparate objects.
• In 2006, the International Astronomical Union officially adopted a
resolution defining planets within the Solar System. This definition
has been both praised and criticized, and remains disputed by some
• There are Eight planets in our Solar System and the other three are
referred to as Dwarf Planets.
The term dwarf planet was adopted in 2006 as part of a three-way
categorization of bodies orbiting the Sun, brought about by an
increase in discoveries of trans-Neptunian objects that rivaled
Pluto in size.
The IAU currently recognizes five dwarf planets—
Ceres, Pluto, Haumea, Makemake and Eris. However, only two of
these bodies, Ceres and Pluto, have been observed in enough
detail to demonstrate that they fit the definition. Eris has been
accepted as a dwarf planet because it is more massive than Pluto.
Dwarf Planet, Eris
Our Planet EARTH
• The Earth is the third planet from the Sun, and the densest and
fifth-largest of the eight planets in the Solar System. It is also the
largest of the Solar System's four terrestrial planets. It is
sometimes referred to as the World, the Blue Planet.
• At present, Earth provides the only example of an environment
that has given rise to the evolution of life. Highly energetic
chemistry is believed to have produced a self-replicating molecule
around 4 billion years ago and half a billion years later the last
common ancestor of all life existed. The development of
photosynthesis allowed the Sun's energy to be harvested directly
by life forms; the resultant oxygen accumulated in the atmosphere
and formed a layer of ozone in the upper atmosphere.
• A comet is an icy small Solar System body that, when close enough
to the Sun, displays a visible coma (a thin, fuzzy, temporary
atmosphere), and sometimes also a tail.
• These phenomena are both due to the effects of solar radiation
and the solar wind upon the nucleus of the comet. Comet nuclei
are themselves loose collections of ice, dust, and small rocky
particles, ranging from a few hundred meters to tens of kilometers
• Comets have been observed since ancient times and have
historically been considered bad omens.
• Halley's Comet or Comet Halley is the best-known of the short-
period comets, and is visible from Earth every 75 to 76 years.