Transcript The Hertzsprung-Russell Diagram

The Hertzsprung-Russell Diagram
Organizing Star Property Data
The H-R Diagram
The “H-R” Diagram was invented around
1910 to organize stars based on their
properties.
The diagram is a graph.
Vertically the scale is increasing Luminosity
Horizontally the scale is Spectral
Class/Temperature
From Hot (O class) to Cool (M class).
H-R
Diagram
Notice there
are 4 groups:
Most Stars
are “Main
Sequence”
Others are:
White
Dwarfs,
Giants and
Supergiants
About the Groups
Most stars lie in the main sequence because if a star is
hotter it is brighter.
Thus you would expect stars of the same size but
different temperatures to form a diagonal line since
“hotter means brighter”
That Main-Sequence is steeper than a ‘same-size
diagonal” shows that larger mass ‘normal’ stars are
hotter…and thus ‘burn’ fuel fast, and have short lives
White Dwarfs are hot, but not that bright, so they must
be small.
Giants and Supergiants are cool, but bright so they
must be very large.
The Instability Strip
On the H-R
Diagram
Cepheid &
RR Lyrae
Variable
Stars are
found in an
area called
the
“Instability
Strip”