 channel for physics please subscribe my channel hello and welcome back to another episode of physics partner today I brought a very very interesting topic related to cosmos and astrophysics I'm talking about the Hertzsprung Russell diagram which is known as HR diagram stars are like humans they have similarities and differences with each other but all have a finite lifetime royal observatory greenwich astronomers explain how stars can be categorized and their evolution studied by tracking their movement across a very important graph in stellar evolution the Hertzsprung Russell diagram let's have a look on a history of HR diagram the Hertzsprung Russell diagram which is known as HR diagram is one of the most important tools in the study of stellar evaluation developed independently in early 1900 by Eugenair Hertzsprung and Henry Norris Russell it plots the temperature of stars against their luminosity I'm talking about the theoretical HR diagram depending on its initial mass every star goes through specific evolutionary stages dictated by its internal structure and how it produces energy each of these stages corresponds to a change in the temperature and luminosity of the star which can be seen to move the different regions of HR diagram as it evolves this reveals the true power of HR diagram astronomers can know a star's internal structure evolutionary stage simply by determining its position in the diagram let's do an interactive activity about HR diagram this HR diagram on your screen shows a group of stars in various stages of their evolution by far the most prominent features in the main sequence which runs from upper left you can see here hot to luminous stars to the bottom right which is cool and faint stars of the diagram the giant branch is also well populated and there are many white dwarfs you can see here there are three main regions of HR diagram the main sequence which is the absolutely the main one is stretching from the upper left hot luminous stars to the bottom right cool faint stars dominates the HR diagram on the right of the screen you can see the changes in the luminosity and temperature it is here that stars spend about 90% of their lives burning hydrogen into helium in their cores main sequence star have a Morgan-Keyner luminosity class level labeled 5 number 2 region is a red giant and super giant stars which is considered as luminosity class 1 through class 3 occupy the region above the main sequence they have low surface temperatures and high luminosities which according to Stephen Boltzmann law meaning they have also large radii i'm talking about this region a star enters this evolutionary stage once they have exhausted the hydrogen fuel in the cores and have started to burn helium and other heavier elements region number three white dwarfs so white dwarf stars which is considered as luminosity class d are the final evolutionary stage of low to intermediate mass stars and are found the bottom left of the HR diagram you can see here on the screen these stars are very hot but have low luminosities due to their small sizes i want to conclude with some facts that the sun is found in the main sequence with a luminosity of one and the temperature of around 5400 kelvin astronomers generally use the HR diagrams to either summarize the evolution of stars or to investigate the properties of collection of stars in particular by plotting a HR diagram for either a global or open cluster of stars astronomers can estimate the age of the cluster from where stars appears to turn off the main sequence so that's all for today i hope it is very informative and useful for you thank you very much for your time take care of yourself and see you in the next video goodbye