Topic 4 - Stars and Planets

• Describe the theory of how the solar system formed.

  Formed from a cloud of dust and gas (Nebula), gravity causes the cloud to compress, the cloud spins. Temperature increases and eventually fusion starts - this forms a star. Solar wind pushes gas particles far away which form gas planets, rock particles are not pushed as far and create rocky planets.
• Describe the object at the centre of our solar system.

  A star (main sequence yellow dwarf).
• What is the order of the planets starting with the furthest from the sun?

  Neptune, Uranus, Saturn, Jupiter, Mars, Earth, Venus, Mercury.
• Between which two planets is the asteroid belt located?


  Mars and Jupiter.
• What types of objects are located in the asteroid belt?

  Asteroids and at least one dwarf planet (Ceres).
• Name the 'rocky' planets.


  Mercury, Venus, Earth, Mars.
• Name the 'gas giant' planets.

  Jupiter, Saturn, Uranus, Neptune.
• Describe the orbit of a comet.

  Highly elliptical (close to the sun at one part of the orbit and further than Pluto on the other side of the orbit).
• What is the relationship between orbital time and distance from the Sun?

  Further a planet is from the sun the longer it takes to orbit (it's year is longer).
• What is meant by the term 'planetary system'?


  A system of planets, moons, asteroids, comets that orbit a star.
• What is meant by the term 'galaxy'?


  Millions of planetary systems held together by gravity (orbits a supermassive black hole).
• Place the following in order starting with the smallest: Planetary system, Moon, Universe, Asteroid, Planet, Galaxy, Star.

  Asteroid, Moon, Planet, Star, Planetary System, Galaxy, Universe.
• What is the meaning of 1 A.U.?

  Astronomical unit - the distance from the Earth to the Sun.
• What is a light year?


  The distance light travels in one year.
• How long does it take light to travel 20 light minutes?

  20 minutes
• Describe star birth.

  (SEE FORMATION OF THE SOLAR SYSTEM)
• What is the process that occurs in the core of a main sequence star and what are the conditions needed?

  Fusion - heat and pressure needed.
• If the star is not large enough to fulfil the conditions above then what type of star is formed?

  Brown or Black Dwarf.
• While a star is on the main sequence describe the forces acting on the star.

  Radiation pressure out is equal to gravity in.
• What will happen to our sun when fusion stops?

  It will expand to form a red giant, it will then fuse heavier elements than hydrogen. This stops at iron - then the star will rapidly shrink leaving a planetary nebula and a white dwarf star.
• Describe all possible star deaths from stars much larger than our Sun.

  Form a red hyper giant, and then create a supernova and leave behind a neutron star or black hole.
• Why does fusion stop when it reaches iron?

  Takes too much energy to fuse iron atoms.
• How do elements heavier than iron get made?

  Supernova explosions provide the high energy required to create the heavier elements.
• Explain why the planets orbit the sun in their current order.

  Solar wind