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The Hertzsprung – Russell Diagram The HR diagram Developed by Einar Hertzsprung and Henry Russell Relationship between absolute mag. and the temperature of stars A star’s position on the diagram tells about size, color, and temp. Also is an evolutionary guide of a star’s life Positioning on the HR Diagram Main sequence stars – Upper left corner to lower right corner 90% of stars are located along the main sequence Upper left – blue/blue-white, large mass, bright, hot Lower right – red, small, dim, cool Sun is located in the middle of the main sequence Positioning (con’t) Red Giants and Super Giants – Above and to the right of the main seq. Very bright, red in color, very large, cool in temperature Brightness of stars are due to their enormous size Positioning (con’t) White Dwarfs – Below the main seq. and centered Not actually white Very small (Earth size), dim, small mass Stellar Evolution and The HR Diagram The position of a star indicates where it is along its evolution Sequence depends on star’s mass 2 types of evolutionary sequences – Sun size and smaller – 10x the Sun’s mass Stellar Evol. and the HR diag. (con’t) Sun sized star’s 1. Interstellar cloud 2. Protostar – nuclear fusion begins here 3. Main sequence – 90% of life time 4. Red Giant –large, cooler 5. Yellow Giant- often variable in brightness 6. 2nd Red Giant – larger than 1st red giant 7. White Dwarf Stellar Evol. and the HR diag. (con’t) 10x the Sun’s Mass 1. Interstellar cloud 2. Protostar- nuclear fusion begins here 3. Massive Main Sequence Star- larger and brighter than the Sun 4. Pulsating Yellow 5. Super Red Giant 6. Supernova – Explosion, new nebula formed 7. Black hole or Neutron Star