The Universe – General Concept Notes with PDF
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Cosmology and the Universe
The Big Bang Theory
- It explains the origin of the universe.
Components of the Universe
- Galaxies: A system of stars.
- Milky Way: Our galaxy is classified as a Spiral Galaxy.
- Solar System’s Motion: The Sun takes approximately 25 crore (250 million) years to revolve around the center of the Milky Way galaxy.
Stars and Their Properties
General Properties
- The colour of a star indicates its temperature.
- A group of stars arranged in a particular shape is called a constellation.
- There are 88 constellations in the sky.
Star Death and Extreme Objects
- Supernova: A dying star that explodes.
- Black Hole:
- An astronomical entity with such a strong gravitational field that it does not allow even light to escape, making it invisible to telescopes.
- This property is due to its extremely high density.
- Chandrasekhar Limit: The mass limit beyond which stars suffer internal collapse and can become neutron stars or black holes.
- The Black Hole Theory was propounded by S. Chandrashekhar.
Specific Stars and Observations
- Betelgeuse: A distant star whose surface was captured in detail for the first time by the Hubble Space Telescope.
- From space (e.g., a spacecraft), the sky appears black, and stars do not twinkle.
Astronomical Measurements and Concepts
Units of Measurement
- Light Year: A unit of distance (the distance light travels in one year).
- It is used for measuring the distance between stars.
Time
- Natural Units of Time: A Tropical year, Lunar month, and Day.
- Human-Made Convention: Standard Time is not a natural unit of time.
Terminology
- Related to Space: Terms like Event Horizon, Singularity, String Theory, and Standard Model are related to the observation and understanding of the Universe.
- Not Related to Space: Byte is a unit of digital information.
Celestial Navigation
Pole Star (Polaris)
- Indicates the North direction.
- The group of stars known as Saptarishi (the Big Dipper/Ursa Major) helps in locating the Pole Star.
- Directional Rule: If you face the Pole Star, you are facing North. Therefore, to walk East, you need to keep the Pole Star to your left.
Observer’s Location
- If an observer sees stars rising perpendicular to the horizon, they are located at the Equator.
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