SOLAR SYSTEM : A Part of Milky Way Galax...

A solar system consists of a sun at the center and the eight planets, moons, asteroids, comets, and meteoroids that revolve around it. The gravitational attraction between the Sun and these objects keeps them revolving around it.

In ancient India, it was imagined to be a river of light flowing in the sky. Thus, it was named Akash Ganga.

The sun, the moon, and all those objects shining in the night sky are called celestial bodies. The study of the universe is known as cosmology. The size of the solar system has been estimated to at about 10^5 AU.

The eight planets, namely Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, revolve around the sun in fixed elliptical paths known as ‘orbits’. • Pluto is a dwarf planet • The light-year is a unit of length used to express astronomical distances.

SUN

• The sun is in the center of the solar system. 
• The sun is the ultimate source of heat and light for the solar system 
• The sun is about 150 million km away from the earth. 
• Light takes about 8.5 minutes to reach the Earth from the sun 
• Hydrogen and helium are the main gases present in the sun. 
• The boundary between the Sun’s interior and the solar atmosphere is called the photosphere. It is the visible ‘surface’ of the Sun 
• The core is at the center of the sun. It is the hottest region, where the nuclear fusion reaction takes place to give the sun power 
• The outer layer of the sun’s atmosphere made up of thin hot gases is called the corona. Corona is visible only during a total eclipse of the sun 
• The Sun has a surface temperature of 6000 degrees Celsius 
• The temperature at the center of the sun is around 1.5*10^7 K 

PLANETS

The planets are classified in order of their distance from the sun and based on their characteristics. They are:

1. The inner planets of terrestrial planets or rocky planets. Mercury, Venus, Earth, and Mars are called inner or terrestrial planets. 
2. The outer planets or gaseous planets or giant planets. Jupiter, Saturn, Uranus, and Neptune are called outer or gaseous planets. All eight planets of the solar system move around the sun in fixed paths. These paths are elongated. They are called orbits. A night planet has been recently discovered by NASA named as Carla 

MERCURY 

• Mercury is nearest to the sun and it is the smallest planet in the solar system 
• Mercury has no satellite of its own
• It rotates on its own axis in 58.65 Earth days while it takes 88 Earth days to complete one revolution around the sun
• The sunlight takes 3.2 minutes to travel from the Sun to Mercury
• Mercury has no protective blanket like Ozone around it to prevent us from harmful radiation 

VENUS

• Venus is the second planet in distance from the sun
• Venus is earths nearest planetary neighbor. It is the brightest planet.
• Venus has no moon or satellite of its own. The rotation of Venus on its axis is somewhat unusual. It rotates from east to west. Only Venus and Uranus have this backward direction
• It completes one rotation in 243 Earth days which is the longest day of any planet in our solar system
• The Venus takes 224.7 Earth days to complete one revolution around the sun, and it has no natural satellites.
• Venus is 0.7 astronomical units away from the sun
• Venus is considered as ‘Earth’s-twin’ because its size and shape are very much similar to that of the earth. It’s also called as ‘Earth sister’
• Venus is known as the evening star as well as Morning star
• Venus is hotter than Mercury because Venus has an atmosphere which is thicker and made almost entirely of carbon dioxide.
• The sunlight takes 6 minutes to travel from the sun to Venus

THE EARTH

• The earth is the third nearest planet to the sun. In size, it is the fifth-largest planet
• The axis of rotation of the Earth is not perpendicular to the plane of its orbit. The Earth is 23.5 degrees tilted on its axis and thus makes 66.5 degrees angle. The tilt is responsible for the change of seasons on the Earth. The Earth has only one moon.
• The Earth rotates from west to east
• It is also known as the ‘Blue Planet’ because of the presence of water.
• Earth has only one natural satellite called the Moon.
• The Earth takes 365.25 days to complete one revolution around the Sun. It takes 23 hours 56 minutes and 4 seconds for the earth to complete one rotation on its axis
• The sun light takes about 8.3 minutes to reach the earth
• Earth has a protective blanket of ozone layer high up in its atmosphere to save life from harmful ultraviolet radiations coming from the sun

THE MARS

• Mars is the fourth nearest planet to the sun and it is the second smallest planet in the Solar system
• It is also described as the “Red Planet”. It is reddish due to the presence of iron oxide on its surface
• The landmass of Mars and Earth are very similar
• It takes 24 hours and 37 minutes to complete one rotation on its axis and its takes 687 days to complete one revolution around the Sun
• Mars has two satellites namely Phobos and Deimos.

THE JUPITER

• Jupiter is the largest planet in the solar system. It is made primarily of gases and is therefore known as ‘Giant Gas planet’
• Jupiter is also known as winter planet
• It takes 9 hours 55 minutes to complete one rotation on its axis and it takes 11.86 years to complete one revolution
• Jupiter has the shortest day in the solar system.
• Jupiter has a faint ring system around it. They are mostly comprised of dust particles
• Jupiter has 67 confirmed satellites orbiting the planet. Ganymede, the satellite of Jupiter, is the largest natural satellite in the solar system (even bigger than the planet Mercury)

THE SATURN

• Saturn is the sixth planet from the sun and the second largest planet in the solar system. Saturn is called as the Ringed Planet
• Saturn is the only planet in our solar system whose average density is less than water.
• The Saturn has 30 rings and 53confirmed natural satellites
• The Saturn takes 10 hours 34 minutes to complete one rotation on its axis and it takes 29.4 years to complete one revolution around the sun
• Titan is Saturn’s largest moon and the second largest (after Ganymede of Jupiter) in the solar system. It is the only moon in the solar system with clouds and a dense, planet-like atmosphere

THE URANUS

• Uranus is the seventh planet from the sun and it is not visible to the naked eye.
• Uranus rotates on its axis from east to west
• Uranus is inclined on its axis at an angle of 98 degrees.
• Hydrogen, helium and methane are the major gases of its atmosphere.
• It is very cold due to its great distance from the sun
• This planet appears greenish in color because of methane gas present in its atmosphere
• Uranus also has rings and twenty-seven satellites
• Uranus is the first planet to have been discovered by the use of a telescope

THE NEPTUNE

• Neptune is the eighth planet from the sun.
• It takes 16 hours to complete one rotation on its axis and it takes nearly 165 years to revolve around the sun.
• It is the coldest planet in the Solar System because it is the farthest planet from the Sun.
• It has 13 natural satellites and 5 rings
• Neptune is surrounded by methane rings of subzero temperature