Summary
Stars are massive celestial bodies composed primarily of hydrogen and helium, undergoing nuclear fusion to emit energy. The Universe, which began with the Big Bang, is expanding, as evidenced by the redshift of light from distant galaxies.
- Star — a massive, luminous sphere of plasma held together by gravity.
Example: The Sun is a star. - Galaxy — a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.
Example: The Milky Way is our galaxy. - Light-year — the distance that light travels in one year in a vacuum.
Example: One light-year is approximately 9.5 × 10^15 meters. - Redshift — an increase in the wavelength of light from an object moving away from the observer.
Example: Light from distant galaxies appears redshifted. - Big Bang Theory — the theory that the Universe originated from an extremely hot and dense state and expanded over time.
Example: The Universe started about 14 billion years ago with the Big Bang.
Exam Tips
Key Definitions to Remember
- Star
- Galaxy
- Light-year
- Redshift
- Big Bang Theory
Common Confusions
- Confusing light-year as a unit of time instead of distance
- Misunderstanding redshift as a change in speed rather than wavelength
Typical Exam Questions
- What is a light-year? A light-year is the distance light travels in one year.
- What evidence supports the Big Bang Theory? The redshift of light from distant galaxies and the Cosmic Microwave Background Radiation.
- How does nuclear fusion occur in stars? Hydrogen nuclei fuse to form helium, releasing energy.
What Examiners Usually Test
- Understanding of the life cycle of stars
- Knowledge of the structure and components of the Universe
- Ability to explain the evidence for the expanding Universe