6.2.2

Galaxies

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Galaxies

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What is a galaxy?

  • A galaxy is a huge collection of stars, dust, and gas, all held together by gravity.
  • Each galaxy contains billions of stars, and often billions of planets too.
  • The Sun is one star among billions in our galaxy, the Milky Way.
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The Milky Way

  • The Milky Way is a spiral-shaped galaxy containing about 100–400 billion stars.
  • Other stars in the Milky Way look much dimmer than the Sun because they are much further away from Earth.
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Light-years

  • Distances in space are so large that we use light-years instead of kilometres.
  • One light-year is the distance light travels in one year in a vacuum.
    • One light-year is equal to 9.5 × 1012 km.
  • Light from nearby stars takes years to reach us, while light from galaxies beyond the Milky Way takes millions or even billions of years.

Jump to other topics

1Motion, Forces & Energy

1.1Physical Quantities & Measurement Techniques

1.2Motion

1.3Mass & Weight

1.4Density

1.5Forces: Effects of Forces

1.6Forces: Turning Effects of Forces

1.7Forces: Centre of Gravity

1.8Momentum

1.9Energy, Work, & Power: Energy

1.10Energy, Work & Power: Work

1.11Energy, Work & Power: Energy Resources

1.12Energy, Work & Power: Power

1.13Pressure

2Thermal Physics

3Waves

4Electricity & Magnetism

4.1Simple Phenomena of Magnetism

4.2Electrical Quantities: Electric Charge

4.3Electrical Quantities: Electric Current

4.4Electromotive Force & Potential Difference

4.5Electrical Quantities: Resistance

4.6Electrical Energy & Electrical Power

4.7Electric Circuits: Circuit Diagrams & Components

4.8Electric Circuits: Series & Parallel Circuits

4.9Electric Circuits: Action & Use

4.10Electrical Safety

4.11Electromagnetic Effects: Electromagnetic Induction

4.12Electromagnetic Effects: The A.C. Generator

4.13Magnetic Effect of a Current

4.14Force on a Current-Carrying Conductor

4.15Electromagnetic Effects: The D.C. Motor

4.16Electromagnetic Effects: The Transformer

5Nuclear Physics

6Space Physics

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