Learning Outcomes:
- Understand different theories regarding the origin and structure of the universe.
- Comprehend the components of the universe, including galaxies, stars, and planetary systems.
- Gain insight into the structure, characteristics, and components of the Solar System.
- Identify the features of celestial bodies like planets, stars, asteroids, comets, and meteors.
The universe consists of all celestial bodies including stars, planets, satellites, asteroids, meteors, comets, dust, and gases. The study of these bodies is known as astronomy, with astronomers being the scientists who specialize in this field. The universe has been a subject of fascination, leading to various theories about its origin and structure.
The understanding of the universe has evolved, primarily through two main categories of theories:
Important Note: Recent experiments at the Large Hadron Collider (LHC) aim to recreate post-Big Bang conditions for deeper insights.
The age of the universe is approximately 13.7 billion years, based on CMBR measurements. The solar system is estimated to be 4.5 billion years old. The age is calculated by:
The fate of the universe hinges on the interplay between expansion momentum and gravitational pull. If the density is below a critical level, it will expand indefinitely; if higher, a Big Crunch will occur.
The universe is structured in a foamy manner, consisting of filaments, superclusters, and galaxy groups. Visible parts concentrate in certain regions, enclosing vast voids. The universe’s components include:
Important Note: The visible matter‘s composition has remained relatively constant since the universe’s inception.
A galaxy is a massive star group, existing in diverse sizes and shapes. Key types include:
The Milky Way, our galaxy, is a spiral type, containing approximately 100 billion stars and a supermassive black hole at its core.
A star is a luminous body of gases undergoing nuclear fusion. The Sun is our nearest star, taking 8.3 minutes for its light to reach Earth. Stars exist in varying forms:
Stars like the Sun undergo transformations into red giants, white dwarfs, and potentially black holes depending on their mass.
Concept: The Chandrasekhar Limit states that stars exceeding 1.44 solar masses cannot remain stable as white dwarfs.
Stars form in nebulae and undergo several phases:
The Solar System is dominated by the Sun, around which eight planets revolve, alongside their satellites, dwarf planets, asteroids, and comets.
The Sun forms 99.9% of the Solar System’s mass and is approximately 5 billion years old. It undergoes nuclear fusion, converting hydrogen to helium, producing vast energy.
Concept: The Goldilocks Zone refers to the habitable distance from a star, where a planet’s surface can sustain liquid water.
The Solar System’s planets fall into two categories:
Important Note: Pluto, once the ninth planet, was reclassified as a dwarf planet in 2006.
| Category | Inner Planets | Outer Planets |
|---|---|---|
| Composition | Rocky surfaces | Gaseous bodies |
| Moons | Few or none | Many, often with rings |
| Atmosphere | Thin, varied composition | Thick, primarily hydrogen and helium |
Found primarily between Mars and Jupiter, these rocky bodies vary in size. The largest, Ceres, is around 1000 km in diameter.
Have highly elliptical orbits and display tails when near the Sun. Halley’s Comet appears every 76 years.
Small objects entering Earth’s atmosphere, often visible as shooting stars. If they survive entry, they are called meteorites.
Important Note: Meteor showers occur when Earth passes through a comet’s tail.
Exoplanets have been found in systems like TRAPPIST-1, some of which lie in the habitable zone.
MCQ: What accounts for most of the universe’s composition?
- Visible matter
- Dark matter
- Dark energy
- Hydrogen
Correct Answer: 3. Dark energy