THEORY EXAMINATION (SEM–IV) 2016-17 SPACE SCIENCE

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

(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.