- The collective form of microscopic molecules to countless galaxies (group of countless stars)
- Study of the Universe is called Cosmology
- Diameter: 10⁸ Light Years
- Unit of Distance: 1 Parsec = 3.26 Light Years
13.7 Bn yrs
Origin of Universe
4.5 Bn yrs
Origin of Solar System
10⁸ LY
Diameter of Universe
- Systematic study of the universe started by Claudius Ptolemy
- Large Hadron Collider (LHC) — successful mega experiment by CERN (European Center for Nuclear Research), Year 2010
- Concept of God Particle based on Indian scientist Satyendra Nath Bose's Boson Theory — presented by Higgs (1964 AD)
- Nicolaus Copernicus: Heliocentric Model
⚡ Quick Recall
1 Parsec = 3.26 Light Years · Bose + Higgs → "Higgs Boson / God Particle" (1964)
| Theory | Proponent / Key Details |
|---|
| Big Bang Theory | Universally accepted · 13.7 billion years ago · Georges Lemaître (Proponent, 1927 AD) · George Gamow (Theory explanation) · Fred Hoyle (Gave the term 'Big Bang') |
| Inflationary Theory | Alan Guth |
| Equilibrium / Continuous Creation Theory (Steady State Theory) | Thomas Gold and Hermann Bondi |
| Pulsating Universe Theory | Allan Sandage |
- Phenomenon of redshift in space
- Explosion of supernova in space
- 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).
- Our Solar System (Sun, Earth, planets, satellites, etc.) is part of the Milky Way Galaxy
- Also known as: Mandakini or Akash Ganga
- Shape: Spiral (80% part), Disc-shaped
- Extent: 80 thousand light years
- Mandakini was first observed by Galileo
- Nearest galaxy: Andromeda (Devayani)
- Least known galaxy: Dwarf Galaxy
80,000 LY
Extent of Milky Way
250 Mn yrs
Sun's one revolution around Mandakini's centre
⚡ Quick Recall
Milky Way = Mandakini = Akash Ganga · Nearest Galaxy = Andromeda (Devayani)
- Beautiful organized pattern of stars
- Largest constellation: Hydra
- Cassiopeia: W-shape constellation (Shear – Brightest)
- 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: 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 star (Dog Star) · Proxima Centauri = Nearest star after the Sun
| Bodies | Description |
|---|
| Astronomical Bodies | Celestial bodies that shine in the night sky |
| Nebula (Nebulae) | Clouds of dust and gases (Hydrogen, Helium & Others). Cosmic Nursery (Birthplace of stars) |
| Orion Nebula | The region of the coolest and brightest stars in the Milky Way |
| Quasar | Bright celestial body, located 4–10 billion light years away |
| Super Cluster | Large group of small galaxy clusters |
| Constellation | Group of stars arranged in a certain pattern |
| Supernova or Nova Star | A star formed after the explosion of a giant star (formation of a neutron star) |
| 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 | Fossil star |
| Cygnus | A bright constellation located in the galaxies |
⚠ Exam Trap
Nebula = Birthplace of stars vs Supernova = Death/Explosion of a star — opposite stages of stellar life, often swapped in MCQs.