CSS GSA — Paper 7, Part-I, Section I (Physical Sciences)
Constituents and Structure of the Universe
- Universe: everything that exists — matter, energy, space, time; estimated age ~13.8 billion years (Big Bang origin, supported by cosmic microwave background radiation and Hubble's observation of galactic redshift/expansion)
- Galaxy: a gravitationally bound system of stars, gas, dust, and dark matter; our galaxy is the Milky Way (barred spiral galaxy, ~100,000 light-years across, contains 100–400 billion stars)
- Light Year: a distance unit (not time) — the distance light travels in one Julian year ≈ 9.46 trillion km (9.46 × 10¹² km); used because interstellar distances are too large for km
- Solar System: Sun + 8 planets, dwarf planets (e.g., Pluto), moons, asteroids (mainly Asteroid Belt between Mars & Jupiter), comets (Kuiper Belt, Oort Cloud)
- Order from Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
- Inner/terrestrial (rocky): Mercury–Mars; Outer/Jovian (gas/ice giants): Jupiter–Neptune
- Largest planet: Jupiter; smallest: Mercury; hottest: Venus (greenhouse effect, not Mercury despite proximity to Sun)
- Sun: a G-type main-sequence star, ~4.6 billion years old, ~99.86% of Solar System's mass; energy from nuclear fusion (hydrogen → helium) in its core
- Earth: 3rd planet from Sun; one natural satellite (Moon); only known planet supporting life; axial tilt 23.5° causes seasons
- Astronomical Units:
- AU (Astronomical Unit) = mean Earth–Sun distance ≈ 149.6 million km
- Light Year ≈ 9.46 × 10¹² km (used for interstellar/galactic distances)
- Parsec = 3.26 light-years (used in professional astronomy, based on parallax)
Processes of Nature
- Solar Eclipse: Moon passes between Sun and Earth, blocking sunlight — occurs only at New Moon; types: total, partial, annular
- Lunar Eclipse: Earth passes between Sun and Moon, Earth's shadow falls on Moon — occurs only at Full Moon
- Rotation: Earth spinning on its own axis — period ≈ 24 hours; causes day/night
- Revolution: Earth orbiting the Sun — period ≈ 365.25 days; causes seasons (combined with axial tilt)
- Weather Variables:
- Temperature: heat energy of the atmosphere, measured by thermometer
- Pressure: atmospheric weight per unit area, measured by barometer; decreases with altitude
- Circulation: large-scale movement of air (e.g., Hadley, Ferrel, Polar cells) driven by uneven solar heating and Earth's rotation (Coriolis effect)
- Precipitation: rain, snow, sleet, hail — condensation of atmospheric water vapor falling to surface
- Humidity: amount of water vapor in air; relative humidity = actual vapor content ÷ maximum capacity at that temperature
- Weather vs Climate: weather = short-term atmospheric state; climate = long-term average pattern over 30+ years — a frequently tested distinction
Natural Hazards and Disasters
- Earthquake: sudden release of energy from tectonic plate movement along faults; measured by Richter scale (magnitude, logarithmic) or Moment Magnitude Scale (Mw); intensity measured by Mercalli scale
- Volcanic Eruption: molten rock (magma/lava), ash, gases released through Earth's crust; occurs mainly at plate boundaries (convergent/divergent) and hotspots (e.g., Hawaii)
- Tsunami: series of massive ocean waves usually triggered by undersea earthquakes, volcanic eruptions, or landslides — not caused by wind (unlike normal waves)