About this previous year paper
SPACE SCIENCE (NOE044)
Section-wise Solved Answers & Notes
SECTION – A (10 × 2 = 20 Marks)
Very short & precise answers
(a) Kepler’s laws of planetary motion Planets move in elliptical orbits with the Sun at one focus.
Line joining planet and Sun sweeps equal areas in equal times.
Square of orbital period ∝ cube of semi-major axis.
(b) Galaxy vs Active galaxy Galaxy: Large system of stars, gas, and dust bound by gravity.
Active galaxy: Emits unusually large energy due to active galactic nucleus (AGN).
(c) Meteorites and asteroids
Asteroids: Rocky bodies orbiting the Sun, mainly between Mars and Jupiter.
Meteorites: Fragments of asteroids that reach Earth’s surface.
(d) Black hole and white dwarf
Black hole: Extremely dense object with gravity so strong that even light cannot escape.
White dwarf: Dense stellar remnant with no nuclear fusion, supported by electron degeneracy pressure.
(e) Radio-quiet vs radio-loud galaxies Radio-quiet: Weak radio emission.
Radio-loud: Strong radio emission with jets and lobes.
(f) Perturbations of stars
Small deviations in motion of stars caused by gravitational influence of nearby bodies.
(g) Variable star and composite star
Variable star: Brightness changes with time (example: Cepheid).
Composite star: Two or more stars acting as one system (example: binary star).
(h) Role and goal of space science
To understand the universe, origin of celestial bodies, and apply space knowledge for communication, navigation, and climate studies.
(i) Origin and evolution of planetary system
Planetary systems form from rotating clouds of gas and dust, gradually condensing into planets under gravity.
(j) Hubble expansion model
States that galaxies are moving away from each other, and recession velocity is proportional to distance.
SECTION – B (Attempt Any Five) (5 × 10 = 50 Marks)
(a) Harvard classification system
Stars are classified based on surface temperature and spectral lines.
Sequence:
O – B – A – F – G – K – M O → hottest, blue
M → coolest, red Mnemonic: Oh Be A Fine Girl Kiss Me
(b) Supernova
A violent explosion of a star at the end of its life.
Types: Type I – white dwarf explosion
Type II – massive star core collapse
Effects: • Releases enormous energy
• Forms neutron stars or black holes • Creates heavy elements
(c) Quasars vs Microquasars
| Quasars | Microquasars |
|---|---|
| Extremely luminous AGN | Smaller stellar systems |
| Found in distant galaxies | Found in Milky Way |
| Powered by supermassive black hole | Powered by stellar-mass black hole |
(d) Early evolution of universe (Big Bang)
• Universe began from extremely hot, dense state • Rapid expansion (inflation)
• Formation of particles, atoms, stars, and galaxies
(e) Nebular theory of solar system formation
Solar system formed from a rotating nebula of gas and dust.
Steps:
• Nebula collapses • Sun forms at center
• Planets form from remaining material
(f) Classification of stars using H-R diagram
Hertzsprung-Russell diagram plots luminosity vs temperature.
Main groups: • Main sequence
• Giants • Supergiants
• White dwarfs
(g) Corrections to Kepler’s laws
Newton introduced gravitational force law to explain deviations.
F=GMmr2F = \frac{GMm}{r^2}F=r2GMm
Kepler’s laws are approximations valid when one mass dominates.
(h) Life cycle of the Sun and solar winds
Life cycle:
Nebula → Protostar → Main sequence → Red giant → Planetary nebula → White dwarf
Solar wind: Continuous flow of charged particles from Sun affecting Earth’s magnetosphere.
SECTION – C (Attempt Any Two) (2 × 15 = 30 Marks)
Q3. Salient features of galaxy and active galaxy
Galaxy features • Billions of stars
• Gas and dust • Spiral, elliptical, irregular shapes
Active galaxy features
• Bright nucleus • Strong radiation
• Jets and lobes • Supermassive black hole
Q4. Bode’s Law
Bode’s law gives approximate distances of planets from the Sun.
a=0.4+0.3×2na = 0.4 + 0.3 \times 2^na=0.4+0.3×2n
Where n = −∞, 0, 1, 2 …
It explains planetary spacing but is not universally accurate.
Q5. Unification theory of active galaxies
Unification explains different AGN appearances as same object viewed at different angles.
Unification patterns
• Seyfert galaxies • Quasars
• Radio galaxies • Blazars
All involve central black hole + accretion disk + jets.