Exploring the life of stars, the motion of planets, and the origin of the Universe.
Our solar system has one star (Sun), eight planets in elliptical orbits, and moons.
[Image of the solar system showing planetary orbits]Satellites:
1. Natural satellites: Moons (e.g. Earth's Moon).
2. Artificial satellites: Human-made (e.g. GPS, ISS, Hubble).
| Geocentric Model | Heliocentric Model |
|---|---|
| Earth at the centre (Historical). | Sun at the centre (Modern). |
Q1: What happens to the orbital period as a planet gets further from the Sun?
The orbital period increases (it takes longer to complete one orbit).
Nuclear fusion releases energy because mass is converted into energy. This creates outward pressure that balances gravity.
[Image of the life cycle of a star]
Small stars (Sun-sized): Nebula → Protostar → Main Sequence → Red Giant → White Dwarf → Black Dwarf
Massive stars: Nebula → Protostar → Main Sequence → Red Super Giant → Supernova → Neutron Star OR Black Hole.
*Black dwarfs have never been observed because the Universe is not old enough for them to form.
Q1: Why are heavy elements (like Gold or Uranium) found on Earth?
They were created and distributed during a Supernova explosion of a massive star.
Gravity provides the centripetal force that keeps a body in orbit. The force always acts towards the centre of the orbit.
For a stable orbit, if the radius decreases, the orbital speed must increase.
Q1: Why is an orbiting planet said to be accelerating even if its speed is constant?
Because its direction is constantly changing, which means its velocity is changing (Acceleration = change in velocity).
Light from distant galaxies is shifted to the red end of the spectrum (wavelength increases). This is not because galaxies move through space, but because space itself is expanding.
[Image of cosmological red-shift and expansion of space]Q1: What is the Big Bang theory?
The theory that the Universe began from a very small, hot, and dense region.
• Orbits: Draw force arrows pointing towards the centre.
• Red-shift: Show wave lines getting longer/wider for distant galaxies.
• Star Life Cycle: Ensure the split after 'Main Sequence' is clear based on mass.
1. Don't say the Sun will end in a Supernova (only massive stars do).
2. Don't forget: Speed is constant, but Velocity is changing in orbit.
3. Don't say galaxies fly through space; the space between them expands.