P16

• 4 rock planets: Mercury, Venus, Earth, Mars
• 4 gas planets: Jupiter, Saturn, Uranus, Neptune
• The asteroid belt is a concentration of asteroids between Mars and Jupiter
• A main sequence star is a stable star becuase the inward forces of gravity and the outward forces of radiation from the core balance each other
• Red-shift gives evidence that the universe is expanding outwards in all directions, suggesting the universe started with a massive explosion (Big bang theory)
• Cosmic microwave background radiation (CMBR) is the radiation produced by big bang
• Scientists discovered CMBR from microwaves coming from every direction in space
• The stars in a galaxy are only a small % of its total mass. the missing mass is called dark matter
• if density of universe is less than a particular amount, it will expand forever - the Big Yawn
• if density of universe is more than a particular amount, it will stop expanding & go into reverse - the Big Crunch
• If an object moves towards an observer, the wavelength of light decreases, this is known as blue shift
• If an object moves way from observer, wavelength of light increases, this is known as red shift
• Light observed from distant galaxises undergoes redshift
• Red-shift shows us how galaxies are movign away from us
• Blue shift shows how galaxies are moving towards us
• the further away the galaxy, the bigger the redshift
• Doppler effect shows how waves behind source have decreased frequency and increased wavelength and in front of the source they will have decreased wavelength and increase frequency
• Centriperal force is the force needed to keep an object moving in a circle and always acts towards centre of circle
• For a planet or satellite in an orbit around a bigger object, the centriperal force is the gravitational force from the bigger object and acts towards its centre
• The centriperal force is a resultant force so it produces an acceleration. The acceleration acts towards the centre of the orbit
• If distance from object its orbitting decreasses, its speed will increase
• The force of gravity is needed to keep smaller object moving along its orbit
• As an object moves around an orbit, its speed remains constant but its direction continually changes so its velocity changes. It accelerates towards centre of orbit
• objects that are too small to become star can be attracted by a protostar to become planets orbiting the star
• an asteroid is a small rocky object which orbits the sun
• comets are very rocky objects in highly elliptical orbits that become visible as they approach sun.
• comets are made of dust and ice and orbit sun in different orbit to planets. the ice melts when comet approaches sun to form comet's tail
• the gfs around planets is strong enough to have pulled nearby objects except for natural satellites