University:
College
Course:
College Physics
Academic year:

2023
Views:

20

Pages:

3
Author:

anon

IB Physics: E 2.6 – Hertzsprung-Russell Diagram The Hertzsprung – Russell is a diagram which models the relation between the temperature and luminosity of a star. ● On the x-axis, we have Temperature (K) ; ○ Please note, on the x-axis, we can also have spectral class. ● On the y-axis, we have Luminosity (Watts) ○ Please note, on the y axis, we can also have absolute magnitude Here is an example of a Hertzsprung Russell diagram: Some key points you should take from this graph: ● The line of stars that lies diagonally are called main sequence stars ● White dwarf stars are what its name suggests – it’s small ○ If you remember Stefan-Boltzmann Law, L = σAT4 , it suggests that Luminosity is proportional to both surface area and 4th power of area. So as you can see, L is really small, whilst ‘T’ is reasonably large – this suggests that surface area ‘A’ is really small. ○ White dwarfs lie in the bottom left to center, where’s Red dwarfs lie in the bottom right to center – again, you might be tested on this in the exam. ● Red Giants again are what its name suggests – its large. In this graph, it is simply labelled as ‘Giant’, although the IB might ask for ‘Red Giant’ ○ Again, use the law above – as the Luminosity is high, the surface area should also be ‘high’ ● Super Giant: Basically a Giant on steroids – even higher luminosity, so on average even larger surface temperature Another thing you need to appreciate is that the scales on the graph above are NOT linear! The IB loves to ask something like this. Questions that can be asked: I’ve done a lot of research and problems about the Hertzsprung-Russell diagram, and whilst the information above is important, being fully equipped to solving problems about the Hertzsprung Russell diagram is even more important. So, some stuff that comes up generally everytime HR Diagrams appear ● Why star A is larger than star B? You can find this solution in my description of the Stefan-Boltzmann Law seen above – generally, this question comes up 9/10 times. ● Labeling the diagram ● Writing alternative labels for the axes E.g. Spectral class is given, what is an alternative for the x-axis?