- The collective form of microscopic molecules to countless galaxies (group of countless stars)
- Study of the Universe is called Cosmology
- Observable Universe diameter: about 92–93 billion light-years; the full Universe’s total size is unknown.
- Unit of Distance: 1 Parsec = 3.26 Light Years
13.8 Bn yrs
Origin of Universe
4.5 Bn yrs
Origin of Solar System
92–93 Bn LY
Diameter of observable Universe
- Claudius Ptolemy: geocentric (Earth-centred) model
- LHC at CERN (European Organization for Nuclear Research): 7 TeV proton–proton collisions began 30 March 2010.
- Bose: Bose–Einstein statistics and the boson particle class; Peter Higgs: Higgs mechanism/particle prediction (1964).
- Nicolaus Copernicus: Heliocentric Model
⚡ Quick Recall
1 parsec = 3.26 light-years; boson honors Bose, while Higgs refers to the Higgs mechanism and 1964 prediction.
| Theory | Proponent / Key Details |
|---|
| Big Bang Theory | Most accepted model · about 13.8 billion years · Lemaître: expanding-universe model (1927) · Gamow: hot Big Bang/nucleosynthesis · Hoyle: coined Big Bang |
| Inflationary Theory | Alan Guth |
| Equilibrium / Continuous Creation Theory (Steady State Theory) | Hermann Bondi, Thomas Gold and Fred Hoyle (1948) |
| Pulsating Universe Theory | Alexander Friedmann (oscillating/cyclic relativistic models, 1922) |
- Phenomenon of redshift in space
- Classic evidence: Cosmic Microwave Background and primordial light-element abundances, alongside cosmic expansion/redshift.
- Contribution of Edwin Hubble: Concept of Expanding Universe
- Increase in the distance of celestial bodies
⚠ Exam Trap
Don't mix up
Georges Lemaître (proposed Big Bang, 1927) with
Fred Hoyle (only coined the term "Big Bang" — and was actually a Steady State theory supporter, not a Big Bang proponent).
- Beautiful organized pattern of stars
- Largest constellation: Hydra
- Cassiopeia: W-shaped; brightest star commonly identified as Schedar (Alpha Cassiopeiae)
- Cygnus: Cross-shaped constellation
- Orion: Hour Glass shaped (Hunter constellation or Kalpurush) — Brightest star: Rigel
- Group of seven bright stars
- Visible in the first quarter of the night in summer season
- Third largest constellation in the sky
- Also known as Big Bear, formed by Ursa Major
- Pole Star is a member of the Ursa Minor (Little Bear) constellation
- Located in the north direction
- Helps in navigation at night
⚠ Exam Trap
Ursa Major (Saptarishi / Big Bear) ≠ Ursa Minor (Little Bear, contains the Pole Star) — exams test this pairing carefully.
- Colour of a star — defined by its temperature
- Nearest star to Earth: Sun
- Brightest star in the night sky: Sirius / Dog Star
- Nearest star after the solar system: Proxima Centauri
- Supernova: Explosion of stars
- Chandrasekhar Limit: 1.44 solar mass — the upper mass limit of a white dwarf star
Chandrasekhar Limit
1.44 Solar Mass
⚡ Quick Recall
Sirius = brightest night-sky star;
Proxima Centauri = nearest star to the Sun.
| Bodies | Description |
|---|
| Astronomical Bodies | Natural objects such as stars, planets, nebulae and galaxies; not all produce their own light |
| Nebula (Nebulae) | Clouds of dust and gases (Hydrogen, Helium & Others). Cosmic Nursery (Birthplace of stars) |
| Orion Nebula | Nearby major star-forming region, about 1,300 light-years away |
| Quasar | Extremely luminous active galactic nucleus powered by matter accreting onto a supermassive black hole |
| Super Cluster | Large group of small galaxy clusters |
| Constellation | Group of stars arranged in a certain pattern |
| Supernova or Nova Star | Supernova: catastrophic stellar explosion; nova: thermonuclear surface outburst on a white dwarf in a binary system |
| Black Hole | A dense gravitational region from which even light cannot pass through |
| Higgs Boson | "God Particle" — the fundamental particle of physics |
| Red Giant | Giant star formed when hydrogen in the core of a star is exhausted |
| White Dwarf | Dense stellar remnant left by a low- or intermediate-mass star |
| Cygnus | Constellation associated with the Northern Cross pattern |
⚠ Exam Trap
Nebula = Birthplace of stars vs Supernova = Death/Explosion of a star — opposite stages of stellar life, often swapped in MCQs.