hello and welcome to today's lesson on hearthstone russell diagrams which is part of the astrophysics or a topic in aqa a level physics so in today's lesson we're going to try and understand her sprung muscle diagrams so if we've been successful and learned in today's lesson we should be able to know the general shape of the hurst removal diagram determine the part of the stellar life cycle from the hurst removal diagram and determine the axis and the scale of a hurst promotional diagram now in 1911 it was realized that if we plot the spectral class against the absolute magnitude of stars then the stars could collate into distinct areas so a hertz progressive diagram is essentially a plot of the luminosity of stars against their surface temperature and a great deal of information about the probes of the stars can be obtained from it so this is a scatter graph of the luminosity of a star compare compared to the sun against the surface temperature which is worked out by the vine displacement law and the stefan law now both scales are logarithmic and was developed independently by two separate astronomers hertzsprung and russell now they developed the graph independently of each other in the years 1911-1913 and they're giving joint credit in graphs of this types are called her strong russell diagrams in their honor so as the surface temperature in the her in the star is closely to the spectral class we can either place the surface temperature or the spectral class on the x-axis of a hurst removal diagram whilst the y-axis is a measure of the brightness of a star its absolute magnitude now in our in our scale we have very bright at the top and very dim at the bottom now what we know from absolute magnitude tells us that very bright is a very negative value whilst a very dim is a very positive value so because we've got to remember the magnitude scale system now you've got to be able to recall the maximum and minimum values of this plot for a standard hurstbound russell diagram now a standard hurst removal diagram goes from plus 15 at the dimmest to -10 at the most brightest now the x-axis is a measure of the surface temperature of the star once again we have very hot at the left hand side and we have very cool at the right hand side so we tend to find that it's 50 000 kelvin at the left hand side whilst is 2500 kelvin at the right hand side now you have to be able to recall these values for your examination now just to note this scale is non-linear and just to clarify we've got very hot on the left hand side of our hearthstone whistle diagram and very cold on the right hand side so temperature goes to the left hand side of the diagram so it increases the further left you go so the temperature is scaled in the opposite direction to what you expect from most of the graphs in science now this scale whilst it is non-linear can also be represented with a spectral class with o on the left hand side and m on the right hand side so this leads to the graph in the following areas in the top left hand corner of your hertz register diagram you get bright and hot stars in the bottom left hand corner of your herdspiral muscle diagram we get hot and dim stars in the top right hand corner we get the bright and cool stars and we get the dim and cool cool stars at the bottom right hand corner so we can place the observed stars on this diagram and we get the following areas so just to clarify we'll be we'll be separating out our hurst muscle diagram into the different spectral classes or you can consider it in the different temperatures now you'll notice that the styles on the hearthstone muscle diagram are not randomly scattered they are divided into three principal groupings as you can see here so placing the stars on the hurst promoting diagram scale leads to the following groups now it can be approximated that all of these stars have a roughly the same power output but we've got the red giants at the top right hand corner the main sequence in the band in the middle and the white dwarfs in the bottom left hand corner now let us consider the main sequence first now you've got to be able to place two stars in the main sequence the first one is our own sun which has an absolute magnitude of plus five and a surface temperature of 5700 kelvin so it's in the g type spectral class and you've also got to consider vega which is formed which was the basis of our magnitude system in astronomy so the absolute magnitude of vega is approximately plus five and it has a surface temperature of 10 000 kelvin so it's in the a spectral class now main sequence stars are are in their long live phase where they're fusing hydrogen into helium now our sun is currently on its main sequence now approximately 90 percent of observable stars in our universe are currently on the main sequence now at the top of the main sequence are the hot and luminous blue stars at the bottom are the cool and dim reddish stars now you've also got the red and the red giant and red supergiant group now this region suggests that the stars are bright but they're quite cool now you've got to be able to recognize one star from this region which is beetlejuice now beetlejuice again has an absolute magnitude of approximately plus f minus five and then has a temperature of 3700 kelvin so as a result belongs in that part of your hearthstone russell diagram now we know that and p equals sigma a t to the four so the red color suggests a low temperature so to maintain the power output the area of these particular stars must be large so this tells us that stefan's law can be used to explain why some stars are referred to as giants or some stars referred to as dwarfs so for example a dim star with an absolute magnitude of plus 10 in spectral class b must have a must be much smaller than the much brighter star absolutely -10 in the same spectral class so it allows you to work out the sizes of our different s stars now because we know that p equals sigma 80 to the 4 we know that these stars must be giant because the low temperature indicates that to maintain the power output the area must be large now the red giants are the stars which have moved off the main sequence and the fusion reactions other than hydrogen to helium are happening inside of them now supergiants have massive as masses typically 10 to 100 times that of the sun and are therefore substantially larger and much more luminous than even the red giants now supergiants are hot enough for nuclear fusion reactions to produce carbon and the heavier elements now the final group we need to focus on are the white dwarfs now this region suggests that the stars here are hot but dim now we know that p equals sigma a t to the four so the white color suggests a high temperature so to maintain the power output the area of our star must be quite small so the white color is very important because it indicates that these stars must be dwarfs and have a small air surface area to them now white dwarfs are stars at the end of their lives where all the fusion reactions have stopped and they are slowly cooling down now white dwarfs will eventually cool to the point of amid no heat or no light or no radiation and become black dwarfs which appears to be the end state of all low mass stars now the significance of the hurst reversal diagram is that it tells us that they exist that they're fundamentally are different kinds of stars so when astronomers first saw these groups they were puzzled why were the three distinct types of stars well it was later realized that the stars were at different stages of their life cycle so it allowed astronomers to work out that there was a stellar life cycle now from the hurstbourne russell diagram we can see different stages of stellar evolution how stars are born how they grow old and how they eventually die so this is the stellar life cycle for an average size star step one the star appears starts on the main sequence now the placement of the star on the sequence depends on its size now as the star carries out fusion it moves along on the main sequence ever so slightly now the star will not move up the entire main sequence it won't go from the bottom right to the top left it might shift a small amount on that main sequence diagonal band but it won't move across all of it then the star will become a red giant and move across to our red giant section here now again the placement of the star on this sequence is dependent on its size and then finally in step four the star becomes a white dwarf and again the placement of the star on the sequence depends on its size so you can see here our different stages of our stellar evolution for an average sized star so you can see here in a bit bit more clearly the evolution of a star like the sun on the hearthstone russell diagram now just to clarify the herzbrush diagram we cover in aqa a level physics is a slight um simplification so you can see a more thorough version of the hertzberg muscle diagram and this in fact is a lovely image it's a collated hearthstone whistle diagram of all of the stars observed with the visible with visible telescopes in human history and you can see our nice regions in our hearts progressive diagram have formed as following now what you should be able to do is as follows for the hearthstone muscle diagram be sure to state the general shape the main sequence the dwarfs and the giants have axis scales ranging from -10 to plus 15 and the absolute magnitude and 50 000 kelvin to 2500 kelvin if this is the temperature or obafgkm if it's a spectral class now you should be familiar with the position of the sun on the hearthstone whistle diagram and you should have this should be able to show the path of a star similar to our sun on the hurst muscle diagram from formation to white dwarf so if you've been successful and learnt in today's lesson you should be able to state the general shape of the hearthstone muscle diagram determine the part of the stellar life cycle from the hearthstone whistle diagram and then finally determine the axis and scale of the hearthstone russell diagram thank you very much for watching today's lesson on the hurst promotional diagram which is part of the astrophysics topic in aqa a level physics thank you very much for watching and as always have a lovely day