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
Equal Radius Lines
In general the hotter
the star is the
brighter it will be.
Thus you would
expect stars of the
same size but
different
temperatures to
form a diagonal
line called an equal
radius line.
Equal Radius lines can be added to an H-R diagram
About the Groups
White Dwarfs are hot, but not that bright, so they must
be small.
Giants and Red Supergiants are cool, but bright so
they must be very large.
The Main-Sequence is steeper than an “equal radius
line”
This is because large mass main sequence stars fuse
fuel faster,
making them hotter, thus brighter
The Instability Strip
On the H-R
Diagram
Cepheid &
RR Lyrae
Variable
Stars are
found in an
area called
the
“Instability
Strip”