The Solar System

The Solar System is a vast and complex system bound together by the Sun’s gravitational force. Basically, It consists of the Sun, eight planets, their moons, asteroids, comets, meteoroids, and other celestial objects. Our solar system exists for around 10 billion years, evolving over time through cosmic processes.

Galaxy

Galaxies are the fundamental building blocks or units of the universe, each containing billions of stars, gas clouds and dust. They are classified into three main types based on their shape:

• Spiral Galaxies – Have rotating arms and a dense core (e.g., the Milky Way).
• Elliptical Galaxies – Oval-shaped and contain older stars.
• Irregular Galaxies – Lack a definite shape.

The Milky Way: Our Galaxy

• It is spiral galaxy about 100,000 light-years in diameter.
• It rotates slowly in a counterclockwise direction.
• The central region of our galaxy is dense with stars, forming a thick disk-like structure.
• And it is Known as Akash Ganga in Indian mythology.

Stars: The Cosmic Powerhouses

Stars are massive celestial bodies composed mostly of hydrogen and helium, generating immense energy through nuclear fusion.

Life Cycle of a Star:

A star goes through different phases, the details are follows:

1. Nebula – A cloud of gas and dust where a star is born.
2. Protostar – The cloud contracts under gravity, forming a dense core.
3. Main Sequence Star – Nuclear fusion ignites, and the star shines brightly.
4. Red Giant/Supergiant – After exhausting hydrogen, it expands.
5. End Stages:
   • White Dwarf – A small, dense remnant of a low-mass star.
   • Neutron Star – Formed after a supernova explosion.
   • Black Hole – A collapsed massive star with intense gravity.

The Sun, our closest star, is the primary energy source for Earth. The nearest star beyond the Sun is Proxima Centauri, 4.35 light-years away.

Constellations

A constellation is a recognizable pattern of stars in the night sky. Ancient civilizations used them for navigation and storytelling.

• Orion, Big Dipper, and Great Bear are well-known constellations.
• The Great Bear (Ursa Major) contains the Saptarishi (Seven Sages) asterism.

The Sun: Heart of the Solar System

The Sun is a massive ball of hot gases, primarily hydrogen and helium, accounting for 99.8% of the Solar System’s mass.

Structure of the Sun:

Sun consist of the following structures:

1. Core – The powerhouse where nuclear fusion occurs.
2. Radiative Zone – Transfers energy outward through radiation.
3. Convective Zone – Energy moves via convection currents.
4. Photosphere – The visible surface of the Sun.
5. Chromosphere – A hotter layer above the photosphere.
6. Corona – The Sun’s outermost and hottest layer.

Sunspots & Solar Flares

• Sunspots – Dark, cooler areas caused by strong magnetic fields.
• Solar Flares – Sudden bursts of energy that can disrupt Earth’s communication systems.
• Auroras – Beautiful lights in polar skies caused by solar wind interactions.

Solar Cycle

• The Sun’s magnetic field flips every 11 years, leading to changes in sunspot activity and solar storms.

Planets of the Solar System

Planets are celestial bodies that orbit the Sun and reflect its light.

Classification of Planets

• Inner Planets (Terrestrial) – Mercury, Venus, Earth, Mars
• Outer Planets (Gas Giants) – Jupiter, Saturn, Uranus, Neptune
• Dwarf Planets – Pluto and other small celestial bodies

Key Planetary Facts

• Smallest Planet: Mercury
• Largest Planet: Jupiter
• Planets with Rings: Jupiter, Saturn, Uranus
• Earth’s Unique Feature: Only planet known to support life

The Moon: Earth’s Natural Satellite

• Formed 4.6 billion years ago, always showing the same face to Earth.
• Influences ocean tides due to its gravitational pull.
• Moonquakes occur due to Earth’s gravitational effects.

Asteroids: The Minor Planets

• Rocky remnants mainly found in the asteroid belt between Mars and Jupiter.
• Largest Asteroid: Ceres (800 km in diameter).
• Collisions with Earth, though rare, have caused significant impacts (e.g., Lonar Lake, Maharashtra).

Comets: The Cosmic Wanderers

• Composed of ice, dust, and rock, often called “dirty snowballs.”
• When near the Sun, they develop a glowing head and a long tail.
• Halley’s Comet appears every 76 years, next visible in 2062.
• Kuiper Belt & Oort Cloud – Regions where comets originate.

Meteors, Meteoroids & Meteorites

• Meteoroids – Small rock fragments in space.
• Meteors – “Shooting stars” that burn up in Earth’s atmosphere.
• Meteorites – Space rocks that survive the journey and land on Earth.

Exoplanets: Planets Beyond Our Solar System

• Exoplanets orbit stars outside the Solar System.
• Scientists search for habitable exoplanets in the Goldilocks Zone—where conditions are suitable for liquid water.

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Subject: Geography

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