UNIVERSE
- Cosmology: Study of the universe.
- Definition: Totality of everything including physical matter, energy, planets, stars, galaxies, and intergalactic space.
Galaxy
- A vast system of billions of stars, dust, and gases bound by gravity.
- Number: Approximately 100 billion galaxies in the universe, each with about 100 billion stars.
- Milky Way Galaxy: Our galaxy formed after the Big Bang.
- Andromeda: Nearest galaxy to the Milky Way.
Big Bang Theory
- Explosion of concentrated matter 15 billion years ago leading to galaxy formation.
- Cosmic Microwave Background: Radiation believed to fill the universe.
- NASA Missions: Cosmic Background Explorer (COBE) and Wilkinson Microwave Anistropy Probe (WMAP) study this radiation.
Stars
- Heavenly bodies made of hot burning gases.
- Shine by emitting their own light.
Black Hole
- Stars with mass >3 times that of the Sun.
- High gravitational power prevents light from escaping.
Comets
- Made of frozen gases.
- Move in elongated elliptical orbits around the Sun with tails pointing away.
Constellations
- Sky divided into units for astronomers to identify stars.
- Number: 88 known constellations.
Satellites
- Heavenly bodies orbiting planets.
- Moon is Earth’s natural satellite.
The Moon
- Diameter: 3,476 km
- Average Distance from Earth: 384,365 km
- Rotation Speed: 27 days, 7 hours, 43 minutes, and 11.47 seconds
- Revolution Speed: 27 days, 7 hours, 43 minutes, and 11.47 seconds
- Time for Moonlight to Reach Earth: 1.3 seconds
Solar System
The solar system consists of the Sun, eight planets, their satellites (or moons), and thousands of other smaller heavenly bodies such as asteroids, comets, and meteors.
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The Sun is a giant ball of hot plasma at the center, holding the system together with its gravity.
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Planets orbit the Sun in nearly circular paths, each with its own unique characteristics:
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Inner Planets (Rocky or Terrestrial)
- Mercury: Smallest and closest to the Sun, rocky with no atmosphere.
- Venus: Hottest planet, shrouded in thick atmosphere, similar size to Earth.
- Earth: Unique planet with liquid water, supporting diverse life.
- Mars: Cold and dry, with thin atmosphere and two moons.
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Outer Planets (Jovian or Gas Giants)
- Jupiter: Largest planet, gas giant with a Great Red Spot storm and many moons.
- Saturn: Second-largest planet, known for its rings made of ice and rock chunks.
- Uranus: Tilted on its side, ice giant with faint rings and moons.
- Neptune: Farthest planet, ice giant with strong winds and blue color.
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Dwarf Planets:
- Smaller celestial bodies meeting some planetary criteria, like Pluto, Eris, Ceres, and Haumea.
The Sun
- Average Distance from Earth: 149,598,900 km
- Diameter: 1,391,980 km
- Temperature of the Core: 15,000,000°C
- Rotation Speed:
- With respect to the equator: 25.38 days
- With respect to the poles: 33 days
- Time for Sunlight to Reach Earth: 8 minutes and 16.6 seconds
Facts about the Universe
- Biggest Planet: Jupiter
- Biggest Satellite: Ganymede (Jupiter)
- Blue Planet: Earth
- Green Planet: Uranus
- Brightest Planet: Venus
- Brightest Planet outside Solar System: Sirius (Dog Star)
- Closest Star of Solar System: Proxima Centauri
- Coldest Planet: Neptune
- Evening Star: Venus
- Farthest Planet from the Sun: Neptune
- Planet with Maximum Number of Satellites: Saturn (Overtaking Jupiter)
- Fastest Revolution in Solar System: Mercury
- Hottest Planet: Venus
- Densest Planet: Earth
- Fastest Rotation in Solar System: Jupiter
- Morning Star: Venus
- Nearest Planet to Earth: Venus
- Nearest Planet to Sun: Mercury
- Red Planet: Mars
- Slowest Revolution in Solar System: Neptune
- Slowest Rotation in Solar System: Venus
- Smallest Planet: Mercury
- Smallest Satellite: Deimos (Mars)
- Earth’s Twin: Venus
- Only Satellite with an Atmosphere like Earth: Titan
Asteroids (or Planetoids)
- Small planetary bodies that revolve around the Sun.
- Found in between the orbits of Mars and Jupiter.
- Also known as minor planets.
Meteors and Meteorites
- Meteors are also called shooting stars.
- Fragments of rocks coming towards the Earth.
- Formed due to collision among the asteroids.
- Meteors that do not burn up completely in Earth’s atmosphere and land on the Earth are called meteorites.
- Composed of various proportions of a nickel-iron alloy (10% nickel and 90% iron) and silicate minerals.
