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Universe
1. Introduction to the Universe
The universe is the vast expanse that includes all matter, energy, space, and time. It
encompasses everything that exists, from the smallest subatomic particles to the largest
galaxies. The study of the universe is known as cosmology, and it is a crucial topic in
the General Awareness section of the exam.
Key Facts about the Universe:
● Origin: The universe is believed to have originated approximately 13.8 billion
years ago through the Big Bang Theory. This theory suggests that the universe
began as a singularity—a point of infinite density and temperature—and has
been expanding ever since.
● Age: The universe is estimated to be about 13.8 billion years old.
● Size: The universe is immense, containing billions of galaxies, each with billions
of stars. The observable universe is estimated to be about 93 billion light-years
in diameter.
● Composition: The universe is composed of:
○ Ordinary matter (stars, planets, gas, dust): ~4.9%
○ Dark matter: ~26.8%
○ Dark energy: ~68.3%
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2. The Solar System
The solar system is a small part of the universe, consisting of the Sun (a star) and all
the celestial bodies that orbit it, including eight planets, dwarf planets, asteroids,
comets, and meteoroids. The solar system is located in the Milky Way galaxy.
Key Facts about the Solar System:
● The Sun:
○ A yellow dwarf star, primarily composed of hydrogen (73.5%) and helium
(24%).
○ It accounts for 99.86% of the solar system's mass.
○ The Sun generates energy through nuclear fusion, where hydrogen
atoms fuse to form helium.
○ Age: Approximately 4.6 billion years.
● Planets: There are eight planets in the solar system, categorized into two
groups:
○ Terrestrial planets (inner planets): Mercury, Venus, Earth, Mars.
○ Gas giants (outer planets): Jupiter, Saturn, Uranus, Neptune.
● Order of Planets from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn,
Uranus, Neptune.
3. Detailed Information on the Planets
Each planet has distinct features that are frequently tested in exams. Below is a
detailed overview of each planet, focusing on facts commonly asked in exams.
3.1 Mercury
● Position: Closest planet to the Sun.
● Size: Smallest planet in the solar system.
● Atmosphere: No atmosphere, leading to extreme temperature variations.
● Temperature: Ranges from 427°C (day) to -173°C (night).
● Moons: None.
● Rings: None.
● Key Fact: Mercury has a very slow rotation (59 Earth days) and a short year (88
Earth days).
● Focus: Smallest planet, proximity to the Sun, lack of atmosphere.
3.2 Venus
● Position: Second planet from the Sun.
● Temperature: Hottest planet (~460°C) due to a thick atmosphere rich in carbon
dioxide (CO₂), causing a runaway greenhouse effect.
● Rotation: Rotates in the opposite direction (retrograde rotation) to most planets.
● Size: Similar to Earth, often called "Earth’s sister planet."
● Moons: None.
● Key Fact: Venus has the longest rotation period of any planet (243 Earth days).
● Focus: Hottest planet, retrograde rotation, atmospheric composition.
3.3 Earth
● Position: Third planet from the Sun.
● Unique Feature: Only planet known to support life.
● Water Coverage: Approximately 71% of Earth’s surface is covered by water.
● Atmosphere: Composed of nitrogen (78%), oxygen (21%), and trace gases.
● Moons: One (the Moon).
● Rotation: ~24 hours (one day).
● Orbit: ~365.25 days (one year).
● Focus: Life-supporting planet, water coverage, presence of a moon.
3.4 Mars
● Position: Fourth planet from the Sun.
● Color: Known as the "Red Planet" due to iron oxide (rust) on its surface.
● Volcano: Home to Olympus Mons, the largest volcano in the solar system.
● Moons: Two (Phobos and Deimos).
● Water: Evidence suggests Mars once had liquid water.
● Atmosphere: Thin, mostly carbon dioxide.
● Focus: Red color, largest volcano, potential for past water.
3.5 Jupiter
● Position: Fifth planet from the Sun.
● Size: Largest planet in the solar system.
● Composition: Primarily hydrogen and helium.
● Magnetic Field: Strongest magnetic field among the planets.
● Storm: Features the Great Red Spot, a massive storm larger than Earth.
● Moons: Over 79, including Ganymede (the largest moon in the solar system).
● Focus: Largest planet, Great Red Spot, number of moons.
3.6 Saturn
● Position: Sixth planet from the Sun.
● Rings: Famous for its extensive ring system made of ice and rock particles.
● Moons: Over 80, including Titan (larger than Mercury and has a thick
atmosphere).
● Density: Less dense than water; it would float if placed in a large enough body of
water.
● Focus: Ring system, moon Titan, low density.
3.7 Uranus
● Position: Seventh planet from the Sun.
● Rotation: Rotates on its side (tilted at ~98°), making it unique.
● Composition: Often referred to as an "ice giant" due to its composition of water,
ammonia, and methane ices.
● Color: Blue-green due to methane in its atmosphere.
● Moons: 27 known moons.
● Rings: Faint ring system.
● Focus: Tilted rotation, ice giant classification, color.
3.8 Neptune
● Position: Eighth and farthest planet from the Sun.
● Winds: Has the strongest winds in the solar system, reaching speeds of ~2,400
km/h.
● Color: Blue due to methane in its atmosphere.
● Moons: 14 known moons, including Triton.
● Focus: Farthest planet, wind speeds, color.
4. Dwarf Planets
Dwarf planets are celestial bodies that orbit the Sun but do not meet all the criteria to be
classified as full planets. The most notable dwarf planet is Pluto.
Key Facts about Pluto:
● Reclassification: Pluto was considered the ninth planet until 2006, when it was
reclassified as a dwarf planet by the International Astronomical Union (IAU).
● Reason for Reclassification: Pluto does not "clear its orbit" of other objects,
which is a key criterion for planet status.
● Other Dwarf Planets: Include Ceres, Eris, Haumea, and Makemake.
5. Other Important Celestial Bodies
● Asteroids: Rocky bodies primarily found in the Asteroid Belt between Mars and
Jupiter. The largest asteroid is Ceres, which is also classified as a dwarf planet.
● Comets: Icy bodies that develop a glowing tail when they approach the Sun. A
famous example is Halley’s Comet, which is visible from Earth every 76 years.
● Meteoroids, Meteors, and Meteorites:
○ Meteoroids: Small rocky or metallic bodies in space.
○ Meteors: Meteoroids that enter Earth’s atmosphere and burn up, creating
a streak of light ("shooting stars").
○ Meteorites: Meteors that survive the journey through the atmosphere and
land on Earth’s surface.
Key Space Missions and Organizations
● ISRO (ISRO Official):
○ Founded: 1969, Bengaluru.
○ Missions:
■ Chandrayaan-1 (2008): Confirmed lunar water molecules.
■ Chandrayaan-2 (2019): Orbiter successful, lander failed.
■ Mangalyaan (2013): First Asian Mars orbiter.
■ Aditya-L1 (2023): Solar mission.
○ Common questions: Mission names, objectives, launch years.
● NASA:
○ Missions: Apollo 11 (1969, Moon landing), Hubble Space Telescope.
● Others: ESA, Roscosmos.
6. Key Concepts and Definitions
● Light-Year: A unit of distance used in astronomy, representing the distance light
travels in one year (~9.46 trillion kilometers). It is often used to measure vast
distances in the universe.
● Galaxy: A massive system of stars, gas, dust, and dark matter. Our solar system
is located in the Milky Way galaxy, which is a spiral galaxy containing billions of
stars.
● Black Hole: A region in space where gravity is so strong that not even light can
escape. Black holes are formed from the collapse of massive stars.
Multiple Choice Questions (MCQs)
To test your understanding of the universe and the planets, here are 10 MCQs based on
the study material. These questions are designed to reflect the type of questions asked
in exams.
1. What is the approximate age of the universe?
a) 4.5 billion years
b) 13.8 billion years
c) 10 billion years
d) 20 billion years
2. Which planet is known as the Red Planet?
a) Venus
b) Mars
c) Jupiter
d) Saturn
3. What is the largest planet in the solar system?
a) Earth
b) Jupiter
c) Saturn
d) Neptune
4. Which planet has the strongest magnetic field?
a) Earth
b) Mars
c) Jupiter
d) Saturn
5. What is the primary composition of the Sun?
a) Hydrogen and oxygen
b) Hydrogen and helium
c) Carbon and oxygen
d) Nitrogen and helium
6. Which planet is often referred to as Earth’s sister planet?
a) Venus
b) Mars
c) Mercury
d) Neptune
7. What is the process by which the Sun generates energy?
a) Nuclear fission
b) Nuclear fusion
c) Combustion
d) Radioactive decay
8. Which planet has the most extensive ring system?
a) Jupiter
b) Saturn
c) Uranus
d) Neptune
9. What is the smallest planet in the solar system?
a) Mercury
b) Venus
c) Mars
d) Pluto
10.Which of the following is a dwarf planet?
a) Earth
b) Mars
c) Pluto
d) Jupiter
11. How long does light from the Sun take to reach Earth?
a) 2 minutes
b) 4 minutes
c) 8 minutes
d) 10 minutes
12. Who proposed the heliocentric model of the solar system?
a) Galileo Galilei
b) Isaac Newton
c) Nicolaus Copernicus
d) Johannes Kepler
13. Which event occurs when Earth is between the Sun and Moon?
a) Solar eclipse
b) Lunar eclipse
c) Comet passing
d) Meteor shower
14. How many planets orbit the Sun in our solar system?
a) 7
b) 8
c) 9
d) 10
15. Which planets lack natural satellites?
a) Mercury and Venus
b) Mars and Jupiter
c) Saturn and Uranus
d) Neptune and Pluto
16. Who established that planetary orbits are elliptical?
a) Isaac Newton
b) Galileo Galilei
c) Johannes Kepler
d) Nicolaus Copernicus
17. Which planets are adjacent to Earth in orbital distance?
a) Mercury and Venus
b) Venus and Mars
c) Mars and Jupiter
d) Jupiter and Saturn
18. What is the correct order of planets from the Sun?
a) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
b) Mercury, Venus, Mars, Earth, Jupiter, Saturn, Uranus, Neptune
c) Venus, Mercury, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
d) Mercury, Earth, Venus, Mars, Jupiter, Saturn, Uranus, Neptune
19. What is the point in a planet’s orbit closest to the Sun called?
a) Aphelion
b) Perihelion
c) Zenith
d) Nadir
20. What primarily determines a planet’s color?
a) Its size
b) Its distance from the Sun
c) Its surface temperature
d) Its atmosphere composition
21. Which theory suggests the universe began ~13.8 billion years ago?
a) Steady State Theory
b) Big Bang Theory
c) Multiverse Theory
d) String Theory
22. What accounts for ~99% of the solar system’s mass?
a) Planets
b) Asteroids
c) Sun
d) Comets
23. Which planet has the fastest rotation period?
a) Mercury
b) Venus
c) Earth
d) Jupiter
24. What is a black hole primarily known for?
a) Emitting light
b) Having no gravity
c) Strong gravitational force, light cannot escape
d) Being a source of energy
25. Which statement is true about the Moon?
a) It has its own light
b) It is larger than Earth
c) It has no atmosphere
d) It has liquid water
