P7 - Inside Stars

P7 - Inside Stars

1. The Sun

   • Closest star to earth, easy to gather data on
   • Solar telescopes such as McMath-Pierce in Arizona USA study the sun
   • Solar telescopes collect sunlight that is then analysed using the latest technology
   • The sun rotates on its axis once every 27 days
     • This rotation by observing the motion of sunspots
     • The Sun's rotation axis is tilted 7.25 degrees from the axis of the Earth's orbit so we see more of the Sun's north pole september and more of its south pole in March

2. Gas Behaviour

   • Kinetic Theory
     • Particles are constantly moving in random directions
     • They constantly collide and bounce off each other
     • The particles hardly take up any space, most gas is empty space
   • Gases consist of very small particles.
   • Absolute zero - theoretical temperature of 0K, where all movement stops.
     • Kelvin -> Celsius = minus 273
     • Celsius -> Kelvin = Add 273
   • Kinetic energy - anything that's moving has kinetic energy
   • As you increase the temperature of a gas the particles have more energy and they speed up

3. More on Gas Behaviour

   • When gas particles collide, they exert some force, thusly when they are in a sealed container, they collide with the walls, thus creating an outward pressure
   • Putting the same volume of gas in a larger container decreases the pressure, therefore a decrease in volume results in an increase in pressure.
   • Volume of a gas is inversely proportional to its pressure at a constant temperature - e.g. if you halve the volume you double the pressure

4. Fusion

   • E=mc^2
     • E = amount of energy released
     • m = amount of mass LOST
     • c^2 = the speed of light squared
     • Used to calculate energy released during fusion (or fission)
   • Nuclei have to be brought close together to fuse (e.g. in stars hydrogen nuclei fuse to make Helium
     • Only nuclei smaller than iron can fuse, anything larger takes part in fission - see P6
   • High pressure and temperatures needed

5. Star Spectra

   • Continuous spectra contain all possible frequencies
     • Hot objects emit more of one frequency than any other - this is the peak frequency
       • Red has a low frequency, therefore it is a cooler star
         • The sun is a fairly cool star - somewhat yellowy
       • Blue has a high frequency
     • The peak frequency depends on its temperature - the higher the temperature the higher the peak frequency
   • Energy levels in atoms are different for each element, corresponding to the spectra, so astronomers use spectra to work out what stars are made of

6. Stars

   • Stars are born in a cloud of dust and gas (Mostly hydrogen and helium)
     • Gravity causes denser regions to contract into clumps
     • When the clumps become dense enough the cloud breaks up into protostars
     • Protostars continue collapsing under gravity reducing in volume and thus increasing in pressure (See more on gas behaviour)
       • Eventually the temperature at the centre reaches a few million degrees and hydrogen nuclei begin to fuse into helium (See fusion)
         • This releases an enormous amount of energy and creates enough outward pressure to stop gravitational collapse. The star has now reached MAIN SEQUENCE stage