Geography / Solar System

✔ Universe

The universe in commonly defined as the totality of everything that exists, including all physical matter and energy, the planets, stars, galaxies and the contents of intergalactic space.

The study of universe is known as Cosmology.
Cosmology-cosmos (universe) + logos (science) The universe has no limit.

A galaxy is a vast system of 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 (10 galaxies) in the universe, and each galaxy has, on an average, 100 billion stars (10" stars). So, the total number of stars in the universe is 10 to the power 22 stars.

The Milky Way Galaxy is the home of the Earth and our Solar System. It is spiral in shape.
Milky Way Galaxy was formed 5 billion years after the Big Bang.
Latest known galaxy is the Dwarf Galaxy.

According to the modern thought, universe can be classified into two parts namely- (a) Atmosphere and (b) Space.

Origin of the universe is explained by the Big Bang Theory, formulated and proposed by the Belgium astronomer and cosmologist Georges Lemaitre.

All the matter in the universe was originally a 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.

Clumps-of dust and gas in a nebula come together due to gravity and form stars.
Stars are made of hot burning gases.
They emit light of 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.

The solar system consists of the sun, the eight planets and their satellites(or moons), and thousands of other smaller heavenly bodies such as asteroids, comets and meteors.
The Sun is at the center of the solar system and all these bodies are revolving around it.
The gravitational pull of the sun keeps all the planet and other objects revolving round it. Thus, the motion of all the members of the solar system is governed mainly by the gravitational force of the sun.
Planets revolve around the sun is 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 size of solar system has been estimated to at about 10 to the power 5 A.U.
The solar system is dominated by the sun which accounts for almost 99.9% of the matter in the whole solar system.
The sun is also the source of all the energy in the solar system.
Pluto is dwarf planet.
Mercury, Venus, Earth, Mars are called terrestrial planets and Jupiter Saturn, Uranus and Neptune are called gaseous planets.

The Sun is at the center of the Solar System.
Its size is thirteen lakh times as that of the Earth.
It is the nearest star to the Earth.
It is an ultimate source of energy for life on Earth. Its diameter is 14 lakh kms.
It is composed of 71% Hydrogen, 26.5% Helium and 2.5% other elements Hydrogen and Helium are the main gases present in the Sun.
Within the Sun, hydrogen is converted to Helium due to nuclear fusin releasing a tremendous amount of heat and light.
It has a surface temperature of 5778 K or 5504.85°C.
The temperature at the center is around 1.571 x 10' K or 15,000,000°C
Shining surface of the sun is called Photosphere, it appears like a disc, Radiats energy and acts as a source of energy.
The outer layer of sun's atmosphere made up of thin hot gases, is called Corona. Corona is visible only during a total eclipse of the sun (or with a special solar telescope called Coronagraph).
The planet travels with the sun through millions of stars in our galaxy at a speed of about 70,000 Km/hr.
The Sun is about 150 million kms away from the Earth.
Light (at the speed of 3,00,000 km/sec) takes about 8.5 minutes to reach the Earth from the Sun.

These are opaque bodies which continuously revolve around and are lighted by the sun.
There are eight planets in the Solar system.
A ninth planet has been recently discovered by NASA named as Carla.
The sequence of planets according to their distance from the Sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
The sequence of planets according to their size (in descending order i.e. from big to small) is Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury.
Jupiter is the biggest and mercury is the smallest planets of our solar system.

The eight planets have been divided into two groups. All the planets of a particular group have some common features. 'Terrestrial planets' or 'Rocky Planets' and 'Jovian planets' or 'Gaseous planets' (Gas giants) are the two groups of planets.
The four planets nearest to the Sun-Mercury, Venus, Earth, and Mars are called terrestrial planets, because their structure is similar to the earth.
Other four planets-Jupiter, Saturn, Uranus and Neptune are called Jovian planets.

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