Solar system, Stability of Orbital Motions & Satellites

• Where does the Sun lie in the Solar System?


  At the centre of the Solar System
• What percentage of the mass of the Solar System does the Sun make up?


  Over 99%
• How many planets are there in the Solar System?


  8 planets
• What is the gravitational field around planets capable of doing?


  It can pull in all nearby objects except natural satellites
• Why is the gravitational field around a dwarf planet different from that of a planet?


  It is not strong enough to pull in nearby objects
• Name the four rocky planets in the Solar System.

  Mercury, Venus, Earth, and Mars
• Name the four gas planets in the Solar System.

  Jupiter, Saturn, Uranus, and Neptune
• What are moons an example of?

  Natural satellites
• What are artificial satellites?


  Man-made objects that can orbit any object in space
• What is an example of an artificial satellite?


  The International Space Station (ISS)
• What do asteroids and comets do in the Solar System?


  They orbit the Sun
• What is an asteroid?


  A small rocky object that orbits the Sun
• Where does the asteroid belt lie?


  Between Mars and Jupiter
• What are comets made of?


  Dust and ice
• How do comets orbit the Sun?


  In a different orbit than those of planets
• What happens to a comet when it approaches the Sun?


  The ice melts and forms the comet's tail
• What mnemonic helps recall the order of the 8 planets in the Solar System?


  • My Very Excellent Mother Just Served Us Noodles
  • Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
• What was the mnemonic used before Pluto was reclassified as a dwarf planet?


  My Very Excellent Mother Just Served Us Nine Pizzas
• What is our solar system a part of?

  The Milky Way galaxy
• How many stars are estimated to be in the Milky Way galaxy?


  Billions of stars
• What do some stars in the Milky Way galaxy have?


  Planets that orbit them
• How many galaxies are estimated to be in the entire universe?

  More than 100 billion galaxies
• How are planets and moons visible from Earth?


  When they reflect light from the Sun
• How far are the outer regions of the Solar System from the Sun?


  Around $5 \times 10^9 \text{ m}$
• How long does it take for light from the Sun to reach Earth?


  8 minutes
• How long does it take for light from the nearest star after the Sun to reach us?


  4 years
• What is the speed of light?


  $3 \times 10^8 \text{ m/s}$
• How can the time taken to travel a certain distance be calculated?


  By using the equation $time =$$\frac{distance}{speed}$
• What is the time taken for light from the Sun to reach Mercury, given its radius of orbit is $5.8 \times 10^9 \text{ m}$?


  $19.3 \text{ s}$
• Why does light seem to travel instantly in everyday life?


  Because the speed of light is very fast and distances are small
• What does it mean that we see the Sun as it was eight minutes ago?


  It means light takes 8 minutes to reach us from the Sun
• What is a nebula?


  A cloud of dust and gas in space
• How is the Sun formed?


  From massive clouds of dust and gas in space
• What happens to a nebula as it collapses?


  It becomes dense and hot and begins to rotate
• What begins when nuclear fusion starts in a collapsing nebula?


  A dense protostar is formed
• What is the balance of forces in a star called?

  Equilibrium
• What two forces are in equilibrium within a star?

  The force of gravity and the force of pressure
• What happens if the temperature of a star increases?


  The outward pressure will also increase, causing the star to expand
• What occurs if the temperature of a star drops?


  The outward pressure decreases, causing the star to contract
• What elements are formed by nuclear fusion in stars?


  All naturally occurring elements except hydrogen