I'm an astrophysicist and I work on simulating galaxies and studying how they affect their environment a different era in the history of the universe. A star is basically a massive cloud of gas which collapse under its own gravity and the collapse produces heat which starts fusion in its core, which stops it from further collapse. So that's when we say a star is born. So the different types of stars are basically stars of different masses and a different evolutionary stages. Stars at less than about 8% of the mass of the sun become what we call as brown wolves. Stars much bigger than the sun would be giants or blue giants because of the color. And sun as it evolves into a later stage in life it becomes what we call as a red giant. In the night sky some stars are brighter than the others because they're closer to us so they appear bigger and brighter. The other depends on their life cycle so the blue giants and the red giants are much bigger and they produce a lot more light and they become brighter. Every mass star has a different life cycle. Sun has a lifetime of about 10 billion years and currently we are approximately in the middle of it. After about 5 more billion years it would evolve into what we call as a red giant phase. In this phase the core of the sun has finished most of its hydrogen so the hydrogen fusion into helium stops. And only a little bit is left over as a shell just around the core so hydrogen is still burning into helium there but in the core it has stopped. So the core starts contracting but the heat due to the shell causes the rest of the star to expand and the outer layers of the sun could reach much further. The distance of the earth from the sun so we would be a part of it of the sun at some point. Stars might smaller than the sun die as a white dwarf so they just burn out and cool down. Stars much bigger than the sun become supernovae and they explode releasing very high amounts of energy and producing a large number of elements especially much higher than ion. And it's these elements which then become what we call as a star dust where future generations of stars are formed and eventually probably life forms. So that's why we say we are made of star dust. Thanks for watching.