Hertzsprung-Russell Diagrams Astronomy

An H-R Diagram Based on Hipparcos Data

A Modern Version of the H-R Diagram

GENERAL INFO: Plot of luminosity vs. temp or by absolute magnitude vs. spectral class 90% of stars are in a band called the main sequence (our sun is in middle) Other 10% are in upper right and lower left

Blue giants-- upper left part of main sequence BIG, luminous, hot Examples: Rigel

Red dwarfs-- lower right portion of main sequence little, faint, cool Examples: Barnard’s star

White dwarfs-- lower left group OFF of the main sequence little, faint, hot Examples: Sirius B

Red Giants-- upper right portion OFF the main sequence big, luminous, cool Examples: Arcturus, Aldeberan

Red Supergiants-- same as red giants, just bigger Examples: Betelgeuse, Antares

The Mass-Luminosity Relation for Main Sequence Stars

A star’s position on the main sequence is determined by its MASS. Most massive stars are most luminous largest mass of a stable star is ~100 x sun faintest red dwarfs are 1/10 sun’s mass brown dwarf: too small to be a star (almost like Jupiter)

Most stars are… Red giants White dwarfs Red dwarfs Blue giants Main sequence stars

Blue giants? Red giants? White dwarfs? The sun? Red dwarfs? E

Blue giants are… Hot or cool? Big or small? Bright or faint? E

Red giants are… Hot or cool? Big or small? Bright or faint? E

White dwarfs are… Hot or cool? Big or small? Bright or faint? E

Our sun is… Hot or cool? Big or small? Bright or faint? E

Red dwarfs are… Hot or cool? Big or small? Bright or faint? E