[PDF] Universe and Solar System Notes | Parmar SSC + Lucent

These Universe and Solar System Notes are based on Parmar SSC & Lucent Books and are available for download in this post.

UNIVERSE & ASTRONOMY

• Study of Universe → Cosmology
• Branch of science dealing with celestial bodies → Astronomy
• Universe consists of many Galaxies, and a galaxy consists of many Solar Systems.

ORIGIN OF UNIVERSE

• Big Bang Theory → Proposed by George Lemaître (1927) and published in 1931.
• Also known as Big Bang Explosion Theory.
• Universe originated from an infinitely hot and dense single point (Singularity).
• Big Bang occurred about 13.8 billion years ago.
• Led to the formation of galaxies, stars and other heavenly bodies.
• Steady State Theory → Proposed by Fred Hoyle, Hermann Bondi and Thomas Gold.
• Universe is continuously expanding, but its average properties remain unchanged.

GALAXY

• A galaxy is a massive collection of stars, gas, dust and dark matter held together by gravity.
• Our galaxy → (Akash Ganga).
• Milky Way formed after the Big Bang.
• Nearest galaxy to the Milky Way → .
• Solar System is located in the Orion Arm (Orion Spur).

ORIGIN OF SOLAR SYSTEM

• Solar System formed about 4.5 billion years ago.
• A cloud of gas and dust collapsed to form a spinning disk called the Solar Nebula.
• Gravity formed the Sun at the centre, while the remaining material formed planets.
• Dust and gas formed planetesimals, which merged to form planets.
• This is the most widely accepted hypothesis.
• Energy in the Sun is produced by fusion of hydrogen nuclei.
• Planetesimal Theory → Proposed by and (1905).
• Nebular Hypothesis → Proposed by (1755) and expanded by (1796).
• Age of Earth → 4.5 billion years.

SOLAR SYSTEM

• Total planets → 8
• Dwarf planets → 5
• Sun is at the centre of the Solar System.
• Sun is the brightest and nearest star to Earth.
• Sun constitutes about 99.86% of the Solar System’s total mass.
• Copernicus Theory (1543) / Heliocentric Theory → Proposed by .
• States that the Sun is at the centre and planets revolve around it.

CELESTIAL BODIES

• Celestial bodies are objects in space such as planets, stars, moons, asteroids, comets, meteoroids, meteors, meteorites and galaxies.
• Luminous Bodies → Emit their own light. Example: Stars.
• Non-Luminous Bodies → Do not emit their own light. Examples: Moon, Comets, Asteroids, Meteoroids, Meteors and Meteorites.

COMETS

• Large icy objects orbiting the Sun.
• Made of dust, rock and frozen gases such as water, carbon dioxide, ammonia and methane.
• • Appears every 76 years
  • Last seen in 1986
  • Expected again in 2061

ASTEROID

• Rocky, metallic or icy object orbiting the Sun.

METEOROID

• Small rocky or metallic body orbiting the Sun.
• Smaller than asteroids, ranging from dust grains to about 1 metre in size.

METEOR

• When a meteoroid enters Earth’s atmosphere (Mesosphere) and burns, it becomes a Meteor (Shooting Star).
• Quadrantids Meteor Shower is visible in early January.

METEORITE

• If a meteoroid survives atmospheric entry and reaches Earth’s surface, it is called a Meteorite.

THE SUN

• Only star of the Solar System.
• Powerhouse of the Solar System.
• Composition:
  • Hydrogen → 73%
  • Helium → 25%
  • Other elements → 2%
• Distance from Earth → 149.6 million km (15 crore km).
• Speed of Light → 3 lakh km/second.
• Time taken by sunlight to reach Earth → 8 minutes 20 seconds.
• Surface Temperature (Photosphere) → 5800 K (~5600°C).
• Core Temperature → 15.7 million K.

CONSTELLATIONS

• A constellation is a group of stars forming a recognizable pattern in the night sky.
• Every constellation forms an Asterism.
• Ursa Major
  • Also called Great Bear and Saptarishi.
  • Contains the Big Dipper asterism.
• Cassiopeia
  • W-shaped constellation.
  • Brightest star → Schedar (Alpha Cassiopeiae).
• Cygnus
  • Prominent northern constellation with a cross shape.
• Sagittarius
  • Bow-and-arrow shaped constellation.
• Orion (The Hunter)
  • Visible during winter in the northern sky.
  • Brightest star → Rigel.
• Brightest star in the night sky → .
• Nearest star to Earth after the Sun → .

ASTRONOMICAL DISTANCE UNITS

• Light Year
  • Distance travelled by light in one year.
  • 1 Light Year = 9.461 × 10¹² km
• Parsec
  • 1 Parsec = 3.26 Light Years

LAYERS OF THE SUN

• Photosphere → Visible surface of the Sun.
• Chromosphere → Reddish layer above the photosphere.
• Corona → Outermost layer of the Sun’s atmosphere, visible during a total solar eclipse and hotter than the photosphere.

PLANETS

• Terrestrial Planets (Inner Planets) → Mercury, Venus, Earth, Mars
  • Small in size
  • Rocky composition
  • Solid surface
  • Near the Sun
  • Few or no moons
  • No rings
• Jovian Planets (Outer Planets) → Jupiter, Saturn, Uranus, Neptune
  • Very large
  • Gaseous composition
  • No solid surface
  • Far from the Sun
  • Many moons
  • Ring systems present
• Gas Giants → Jupiter, Saturn
• Ice Giants → Uranus, Neptune

MERCURY

• Closest planet to the Sun.
• Smallest planet in the Solar System.
• Diameter → 4,900 km.
• Fastest planet.
• Orbital speed → 172,300 km/hour (47 km/s).
• Revolution period → 88 days.
• No significant atmosphere.
• No natural satellite.

VENUS

• Hottest planet in the Solar System.
• Known as Earth’s Twin.
• Brightest planet in the Solar System.
• Visible during morning and evening.
• Slowest rotating planet.
• Rotation period → 243 Earth days.
• Covered with thick clouds of Sulphuric Acid (H₂SO₄).
• Other names → Morning Star, Evening Star, Lucifer.
• Has no natural satellite.
• Rotates from East to West.

EARTH

• Only known planet that supports life.
• Known as the Blue Planet.
• About 70% covered by water.
• One natural satellite → Moon.
• Highest density among planets → 5.5 g/cm³.
• Closest planet to Earth → Venus.

MARS

• Known as the Red Planet.
• Second smallest planet after Mercury.
• Natural satellites → Phobos and Deimos.
• Thin atmosphere with valleys, craters, deserts and ice caps.
• Olympus Mons is the largest volcano and tallest mountain in the Solar System.
• Height → 22–25 km.
• Length of a Martian day → 24 hours 37 minutes.

ASTEROID BELT

• Located between Mars and Jupiter.
• asteroid → 2006 VP32.
• studied by NASA’s OSIRIS-REx Mission.

JUPITER

• Largest planet in the Solar System.
• Fastest rotation → 9 hours 55 minutes.
• Atmosphere mainly Hydrogen and Helium.
• Third brightest object after Moon and Venus.
• Contains Great Red Spot.
• Has 95 known moons.
• Major moons → Io, Europa, Ganymede, Callisto.
• Known as Galilean Moons.
• Ganymede is the largest moon in the Solar System.

SATURN

• Second largest planet.
• Famous for ring system made of ice and rocky particles.
• Least dense planet → 0.69 g/cm³.
• Can theoretically float on water.
• Has 274 known moons.
• Largest moon → Titan.
• Titan and Enceladus show possibilities of life.
• discovered rings in 1655.
• discovered ring gap in 1675.
• Rotation period → 11 hours.

URANUS

• Known as the Green Planet.
• Green colour due to Methane.
• Discovered by (1781).
• Coldest planetary atmosphere.
• Has at least 27 moons.
• Important moons → Miranda, Ariel, Umbriel.
• Axis tilted by 98°.
• Known as Rolling Planet/Lopsided Planet.
• Rotation period → 17 hours.
• Rotates from East to West.

NEPTUNE

• Farthest planet from the Sun.
• Revolution period → 165 years.
• Rotation period → 16 hours.
• Bluish colour due to Methane.
• Atmosphere mainly Hydrogen and Helium.
• Windiest planet.
• Discovered by and (1846).
• First planet discovered through mathematical prediction.
• Has 14 moons.
• Most famous moon → Triton.
• Has faint rings.

PLANETS IN DECREASING ORDER OF SIZE

• Jupiter → Saturn → Uranus → Neptune → Earth → Venus → Mars → Mercury

MOON

• Earth’s only natural satellite.
• Non-luminous body.
• Radius → 1.74 × 10⁶ m (1,740 km).
• Thin atmosphere called Lunar Exosphere.
• Moonlight takes 1.26 seconds to reach Earth.
• Distance from Earth → 384,000 km.
• Gravity on Moon → 1/6th of Earth’s gravity.
• Only one side is normally visible from Earth.
• Rotation period = Revolution period = 27.3 days.
• Highest point → Mons Huygens (formerly Mt. Leibniz).

SOLAR MISSIONS

• • India’s first solar observatory mission.
  • Launched by .
  • Studies the Sun.
  • Located at L1 Lagrange Point.

LAGRANGE POINTS

• Positions where gravitational forces of two large bodies balance centripetal force.
• Total → 5 (L1–L5).

CHANDRAYAAN-3

• Third lunar mission of .
• Lander → Vikram
• Rover → Pragyan
• Landing site → Shiv Shakti Point
• Landed near the Lunar South Pole.

INTERNATIONAL ASTRONOMICAL UNION (IAU)

• Headquarters →

KUIPER BELT

• Ring-shaped region beyond Neptune.
• Contains asteroids, comets and dwarf planets.
• Pluto is a member of the Kuiper Belt.

PLUTO

• Discovered by .
• Removed from the list of planets by IAU in 2006.
• Classified as a dwarf planet.
• Largest moon → Charon.
• Total moons → 5.
• Revolution period → 248 Earth years.
• Orbit overlaps with Neptune’s orbit.

DWARF PLANETS

• Orbit the Sun.
• Nearly spherical in shape.
• Cannot clear their orbital neighbourhood.

MAJOR DWARF PLANETS

• Pluto → Largest and brightest dwarf planet.
• Eris → Second largest dwarf planet.
• Makemake → Third largest dwarf planet; revolution period about 310 years.
• Haumea → Fastest rotating dwarf planet in the Kuiper Belt.
• Ceres → Located in the Asteroid Belt.

INTERNATIONAL SPACE STATION (ISS)

• Completes one orbit around Earth in 90–93 minutes.

IMPORTANT TERMS

• Supernova → Explosion of a star.
• Pulsar → Rapidly rotating neutron star.
• Black Hole → Region in space with extremely strong gravity from which even light cannot escape.
• Van Allen Radiation Belts → Two concentric belts of charged particles surrounding Earth.