Introduction – Discovering the Secrets of Our Solar System: 

The solar system is a captivating celestial arrangement, consisting of the Sun, its retinue of planets, moons, asteroids, comets, and other celestial bodies. It offers a fascinating glimpse into the vast cosmos and our place within it. The intricate dynamics and diverse features of each solar system member provide valuable insights into the processes of planetary formation and the origins of our home planet, Earth. 

Celestial bodies 

• The sun, the moon and all those objects shining in the night sky are called celestial bodies. 

Stars: Night Sky with Celestial Bodies

• Celestial Bodies: Stars: Some celestial bodies are very big and hot made up of gases. 
• They have their own heat and light, which they emit in large amounts. These celestial bodies are called stars, for example the sun. 
• Navigation by Stars: In ancient times, people used to determine directions during the night with the help of stars. 
• North Star (Pole Star): The North star or the Pole Star indicates the north direction, and always remains in the same position in the sky (Refer Figure 2.3). 

Revealing the Marvels of Our Solar System

• Formation of the Solar System: The nebula from which our Solar system is supposed to have been formed, started its collapse and core formation around 5-5.6 billion years ago and the planets were formed about 4.6 billion years ago. 
• Etymology of “Solar System”: In Roman mythology ‘sol’ is the ‘Sungod’. ‘Solar’ means ‘related to the sun’. 
• The family of the sun is, therefore, called the solar system with the sun as its Head. 
• Components of the Solar System: The sun, eight planets, satellites and  millions of other smaller celestial bodies like asteroids, meteoroids  and huge quantities of dust-grains and gases form the solar system (Refer Figure 2.4). 

Guiding Light: The Sun’s Role in Our Solar Neighborhood

• The Central Role of the Sun: The sun is in the centre of the solar system. 
• Sun’s Characteristics: It is huge and made up of extremely hot gases. 
• Sun’s Characteristics: It provides the pulling force that binds the solar system. 
• Source of Heat and Light: The sun is the ultimate source of heat and light.
• Earth-Sun Distance: The sun is about 150 million km away from the earth. 

Mysteries of the Moon: A Simple Guide to Our Earth’s Natural Companion

• Earth’s Natural Satellite: Our earth has only one natural satellite, i.e, the moon. 
• Moon’s Characteristics: Its diameter is only 1/4th that of the earth. 
  • It appears so big because it is nearer to the earth (about 3,84,400 km away)  than other celestial bodies.

• Orbit and Synchronization: It moves around the earth in about 27 days and takes exactly the same time to complete one spin. As a result, only one side of the moon is visible to us on the earth. 
• Lack of Favorable Conditions for Life: There are no conditions favourable for life.
  • It has mountains, plains and depressions on its surface which cast shadows on the moon’s surface. 
• Surface Features and Phases: It appears in different shapes and at different positions. One can see the full moon night or Poornima only once in about a month’s time. 
  • A fortnight later, one cannot see it at all as it is a New moon night or Amavasya.

Asteroids: Tracing the Remnants of Celestial Explosions in Our Solar Arrangement

• Asteroids in the Solar System: There are numerous other tiny bodies that move around the sun called asteroids(Refer Figure 2.6). 
• Asteroid Belt: They are found between the orbits of Mars and Jupiter. 
• Asteroid Origin Hypothesis: Scientists are of the view that asteroids are parts of a planet which exploded many years back. 

Cosmic events: Meteoroids, Meteors, Meteorites, and the Planetary journey

• The small pieces of rocks which move around the sun are called meteoroids. 

• • Meteor: Sometimes these meteoroids come near the earth and tend to drop upon it and due to friction with the air they get heated up and burn with a flash of light called Meteors. 
  • Meteorite: A meteor without being completely burnt, falls on the earth and creates a hollow called a Meteorite.

Wandering Worlds: Unveiling the Stories of the Eight Planets in Our Solar Symmetry

• Planets in the Solar System: Some celestial bodies do not have their own heat and light and they are lit by the light of the stars. 
• Such bodies are called planets. 
• Origin of the Term “Planet”: The word ‘planet’ comes from the Greek word “Planetai” which means ‘wanderers’.  
• Eight Planets in the Solar System: There are a total of eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. 
• They  get heat and light from the sun and some of them have their moons too.   
• Orbital Paths: All the eight planets of the solar system move around the sun in fixed elongated paths called orbits.

• Inner and Outer Planets: Out of the eight planets, mercury, venus, earth and mars are called the inner planets (also called Terrestrial planets meaning earth-like as they are made up of rock and metals, and have relatively high densities) as they lie between the sun and the belt of asteroids. 
• The other four planets are called the outer planets (also called Jovian means Jupiter-like or Gas Giant planets)(Refer Table 2.3).

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